What is a pending txn?

Excuse me, could you please clarify what exactly is meant by a 'pending transaction' in the world of cryptocurrency? I've come across this term frequently but I'm still a bit hazy on the specifics. Is it a state that a transaction enters into after it's been initiated but hasn't been fully processed or confirmed on the blockchain yet? And if so, what factors can contribute to a transaction remaining in this pending state for an extended period of time?