This is the 142nd most frequent German word.
bleiben
To stay or remain.
Here 'bleiben' is used in its literal sense, meaning 'to stay' or 'to remain at a place'.
Ich bleibe heute zu Hause.
I am staying at home today.
In this sentence, 'bleiben' is used metaphorically to indicate maintaining a mental or physical state, in this case, calmness.
Bleiben Sie bitte ruhig!
Please stay calm!
Here 'bleiben' expresses continuity or persistence of a condition or state, particularly a relationship.