1.75 grams of crack (nominal) which is half a 'game' (3.5 grams) - or 1/8 oz. Crack is normally sold by the 'half' (1/2 gram) which is a tiny little bag of rocks. A half is also called a "$40 piece" (dollar amount may vary) which can be broken down into "$5-$20 pieces" for users who cannot afford more, but they will also pay a much higher rate per gram. A typical, drug-addicted street prostitute will smoke 3.5 grams per day for 3-5 days straight (with no sleep) until the drug, food deprivation and sleep deprivation literally drop her. This is why you see street hookers out at ALL times of the day and night - they need 'food' (more crack). The crack 'energizes' her and makes her feel so good again that she is ready to work some more, to get more crack of course. After a while she becomes insensitive to the high and some dealer/user/pimp will teach her how to inject crack with lemon juice (or vinegar to neutralize the baking soda in the crack) intervenously, to give her a baseline, then smoking will once again give her a buzz. The acid in the lemon juice will eventually burn out her veins the IV will not work any more.
Street hookers use this term to describe a blow job. 'Little' meaning a smaller amount of money than a lay and also less time. It is also less distasteful as they can get what they want (the drugs) quicker, what with no undressing etc. Also easier to do in a vehicle.