It looks like you retain the copyright, but you grant twitter and others (!) the right to display your work without compensation. I'm not a lawyer, though!

"By submitting, posting or displaying Content on or through the Services, you grant us a worldwide, non-exclusive, royalty-free license (with the right to sublicense) to use, copy, reproduce, process, adapt, modify, publish, transmit, display and distribute such Content in any and all media or distribution methods (now known or later developed).

This license authorizes us to make your Content available to the rest of the world and to let others do the same... Such additional uses by Twitter, or other companies, organizations or individuals, may be made with no compensation paid to you with respect to the Content that you submit, post, transmit or otherwise make available through the Services."

https://twitter.com/en/tos