A harlot in the bible is a prostitute. Someone that sells sex in exchange for goods or money.
 And she put her widow’s garments off from her, and covered her with a vail, and wrapped herself, and sat in an open place, which is by the way to Timnath; for she saw that Shelah was grown, and she was not given unto him to wife.
 When Judah saw her, he thought her to be an harlot; because she had covered her face.
 And he turned unto her by the way, and said, Go to, I pray thee, let me come in unto thee; (for he knew not that she was his daughter in law.) And she said, What wilt thou give me, that thou mayest come in unto me?
 And he said, I will send thee a kid from the flock. And she said, Wilt thou give me a pledge, till thou send it?
 And he said, What pledge shall I give thee? And she said, Thy signet, and thy bracelets, and thy staff that is in thine hand. And he gave it her, and came in unto her, and she conceived by him.— KJV, Genesis 38:14-18
We can see that in Judahs dealing with Tamar that plays the harlot. Judah gives her a pledge  and then he is to give her a kid of the flock as a price for coming in unto her. So its a payment for sex. We see also in  that she sat in an open place by the way  so its a street hooker.
 My son, attend unto my wisdom, and bow thine ear to my understanding:
 That thou mayest regard discretion, and that thy lips may keep knowledge.
 For the lips of a strange woman drop as an honeycomb, and her mouth is smoother than oil:
 But her end is bitter as wormwood, sharp as a twoedged sword.
 Her feet go down to death; her steps take hold on hell.
 Lest thou shouldest ponder the path of life, her ways are moveable, that thou canst not know them.
 Hear me now therefore, O ye children, and depart not from the words of my mouth.
 Remove thy way far from her, and come not nigh the door of her house:
 Lest thou give thine honour unto others, and thy years unto the cruel:
 Lest strangers be filled with thy wealth; and thy labours be in the house of a stranger;
 And thou mourn at the last, when thy flesh and thy body are consumed,
 And say, How have I hated instruction, and my heart despised reproof;
 And have not obeyed the voice of my teachers, nor inclined mine ear to them that instructed me!
 I was almost in all evil in the midst of the congregation and assembly.
 Drink waters out of thine own cistern, and running waters out of thine own well.
 Let thy fountains be dispersed abroad, and rivers of waters in the streets.
 Let them be only thine own, and not strangers’ with thee.
 Let thy fountain be blessed: and rejoice with the wife of thy youth.
 Let her be as the loving hind and pleasant roe; let her breasts satisfy thee at all times; and be thou ravished always with her love.
 And why wilt thou, my son, be ravished with a strange woman, and embrace the bosom of a stranger?
 For the ways of man are before the eyes of the LORD, and he pondereth all his goings.
 His own iniquities shall take the wicked himself, and he shall be holden with the cords of his sins.
 He shall die without instruction; and in the greatness of his folly he shall go astray.— KJV, Proverbs Chapter 5
As you can see in verse 8 we should remove our way from her.
Also proverbs 7 below contains verses regarding the harlot.
 My son, keep my words, and lay up my commandments with thee.
 Keep my commandments, and live; and my law as the apple of thine eye.
 Bind them upon thy fingers, write them upon the table of thine heart.
 Say unto wisdom, Thou art my sister; and call understanding thy kinswoman:
 That they may keep thee from the strange woman, from the stranger which flattereth with her words.
 For at the window of my house I looked through my casement,
 And beheld among the simple ones, I discerned among the youths, a young man void of understanding,
 Passing through the street near her corner; and he went the way to her house,
 In the twilight, in the evening, in the black and dark night:
 And, behold, there met him a woman with the attire of an harlot, and subtil of heart.
 (She is loud and stubborn; her feet abide not in her house:
 Now is she without, now in the streets, and lieth in wait at every corner.)
 So she caught him, and kissed him, and with an impudent face said unto him,
 I have peace offerings with me; this day have I payed my vows.
 Therefore came I forth to meet thee, diligently to seek thy face, and I have found thee.
 I have decked my bed with coverings of tapestry, with carved works, with fine linen of Egypt.
 I have perfumed my bed with myrrh, aloes, and cinnamon.
 Come, let us take our fill of love until the morning: let us solace ourselves with loves.
 For the goodman is not at home, he is gone a long journey:
 He hath taken a bag of money with him, and will come home at the day appointed.
 With her much fair speech she caused him to yield, with the flattering of her lips she forced him.
 He goeth after her straightway, as an ox goeth to the slaughter, or as a fool to the correction of the stocks;
 Till a dart strike through his liver; as a bird hasteth to the snare, and knoweth not that it is for his life.
 Hearken unto me now therefore, O ye children, and attend to the words of my mouth.
 Let not thine heart decline to her ways, go not astray in her paths.
 For she hath cast down many wounded: yea, many strong men have been slain by her.
 Her house is the way to hell, going down to the chambers of death.— KJV, Proverbs Chapter 7
A harlot can cause a dart to strike through the liver  and she is a snare  and she can be deadly  She has slayed many strong men and cast down many wounded, so we should not let our hearts decline to her ways [25-26]. A Harlot is the way to hell and death .
A harlot is set apart for pollution.
In thee have they discovered their fathers’ nakedness: in thee have they humbled her that was set apart for pollution. — KJV, Ezekiel 22:10
How should we deal with a harlot ?
We are told to remove our way from the harlot (Proverbs 5:8).