DTC is a clearinghouse used by public companies to facilitate clearing/trading of stock. Rather than keep detailed books of their holders companies use DTC for this purpose. DTC uses a book entry system to track trades and settles each night with MM and trading firms.
The issuer doesn't need to worry about issuing shares and acting as its own transfer agent. DTC does this for them.
I have used DTC over the years and they do a good job. They tend to want to handle large to midsize public companies.
News 
Market Data 
Discover 
