Exclusives?

exclusive means "don't send it out, don't let anyone else read it while i have it". exclusives suck. If an agent wants an exclusive, you can give it, but do let him know if you have other copies out there. Also restrict the time of the exclusive. tell him, i will grant you an exclusive for x number of weeks. after that time i will contact you, and i will resume sending this out depending on your answer. don't just let them have it for how ever long cause agents are slow and you could end up sitting on your hands for months. and then your fingers will fall asleep and that's just icky. Good luck.

What this means is that the agent wants to be the only person considering the (usually) full manuscript. So if any other agent asks to see it you have to tell them that they have to wait. The tradeoff is supposed to be that the agent requesting the exclusive treats the manuscript as a priority and gets back to you by a certain date (one month is often quoted as a period of exclusivity).
If you grant an exclusive you should try very hard to impose a time limit. It is far from uncommon for agents to lose track of time with manuscripts (and sometimes lose track of manuscripts)