Tera is a decentralized application platform. This is akin to an operating system. Tera consists of a repository of programs and data storage integrated into the Internet. The mechanism for publishing programs and data on this platform is free from censorship. The circulatory system is the blockchain.
Steem Dollars are liquid stable-value currency tokens designed to be pegged to $1 USD. Steem Dollars can be traded with STEEM and transferred to other accounts for commerce or exchange.