USDT.e on Avalanche is a token representing USDT on Avalanche that was bridged from the Ethereum blockchain via the Avalanche Bridge.
For example, when sending USDT over the bridge to the Avalanche Network, it will appear as USDT.e once the transaction is completed.
If you don't immediately see the USDT.e after a successful transaction, you may need to add the token to the wallet you are using so it shows your balance of USDT.e.
Note that sending USDT.e back is the same process but in reverse, resulting in USDT.e turning into USDT.
You can swap USDT.e for Avalanche native USDT using DEXs on Avalanche.
For a more in-depth read on how the Avalanche Bridge works, please read the following articles.