A Terms Sheet is one of the final documents that will be developed by parties in a corporate transaction - be that capital raising or other deal.
Beyond the Information Memorandum the Terms Sheet summarises the co factors that will make up the deal.
It becomes a focal point of negotiation, and as such also becomes a simple document to instruct lawyers with. If drafted correctly the Terms Sheet will expand into the full legal contract.
For the very organised, the development and presentation of a Terms Sheet is a high credibility tool to gain the attention of the counter party and lead the deal to a conclusion (hopefully positive one).