A standup is a short meeting — usually held daily — for team members to share their progress, discuss what was achieved yesterday and decide what should be the focus for the coming day.
A standup is also the best time to analyze what is blocking progress and to find solutions on how to move forward.
Some teams take the name literally — encouraging members to stand up — as this helps to keep things brief, focused and to the point. But a standup can also happen when seated!
Standups are vital for productive team communication and, as such, are a fundamental part of the agile development framework.