Q:

What are Forms in Lists? 

What are Forms in Lists?  What are the Forms available in Lists?  And What is "InfoPath"?  How is it related to Forms? 

A:

With regards to SharePoint, there are 3 forms for each list.  These are the NewForm (adding a new item to the list), EditForm (editing an existing item in the list), and the DispForm (or Display Form, which is just viewing the list entry).  With SharePoint Enterprise, you can edit the appearance of how these forms look if you don't like the default SharePoint forms, and this editing is done through Microsoft InfoPath.  You can also set up rules for certain fields (like a Time In cannot be before a Time Out) to make your form safer. 
Now what is InfoPath?  InfoPath is a form designer which allows the designer to establish and create data connections for fields in a SharePoint list, SQL database, etc.  Microsoft actually has 2 InfoPath applications: InfoPath Designer, and InfoPath Filler.  InfoPath Filler basically allows for data to be entered in the published form's fields and submitted to wherever the data connection exists. 
Hope this helps you understand.