I keep hearing about affidavits being used in lieu of depositions...

In general, an affidavit is a statement that the information that a person provided is true to the full extent of their knowledge. You sign an affidavit when you report information on a car loan application, for example. In the case of court documents, an affidavit is a statement of what a witness saw that's related to the case at hand. Someone who provides an affidavit may or may not be called on to give a deposition or to become a witness when the case goes to court, but when producing an affidavit, a witness is not going to be questioned about his or her statement - it's merely a summary of what they experienced. If you're looking at an affidavit, make sure that it's been witnessed and qualified by a notary public or other official. If someone comes to you as a court reporter and plans to offer an affidavit about the case, you'll need to ensure that the signer knows that he is she is making a legally binding statement, and you'll need to verify that the individual is capable of understanding the seriousness of the statement that they are making - and the oath they make that all of the information contained is accurate.

The last answer summed up a lot of it - the whole affidavit being a legally binding statement of what a witness experienced. I just wanted to add that if you are working as a court reporter and someone comes to you asking to prepare an affidavit for them about a case, before they sign the document you produce, make sure that the person reads the statement before signing. After all, they're claiming under penalty of perjury that all of the information is accurate - they should have the chance to give the document a once over to make sure that it is before they submit it to the courts.