Meaning
Something that stops your work until another person or team acts.
Three examples from work
Stand-up
Team leadAny blockers?
DeveloperOne: I'm waiting for access to the staging server.
Planning
PMIs anything a blocker for the release?
QAThe login bug is. Everything else can wait.
Client call
ClientWhy hasn't it moved?
YouThe blocker is the missing API key from your side.