Red Sea & Persian Gulf . Why one is sea & the other is a gulf ?

Question

When to call this or that ? What's the difference ?

Answer 1

If  you are looking for a rationale, you are wasting your time. Why is the Gulf of Mexico only a Gulf while the Caribbean is a sea. Why is Hudson Bay only a bay when it is really an inland sea? Why is the Bay of Biscay only a bay while the Mirtoon Sea is called a sea. Convention, pure and simple. There is no rational reason really for these distinctions.

Answer 2

A sea is a large expanse of saline water connected with an ocean

A gulf usually refers to a large bay that is an arm of an ocean or sea.

Answer 3

Maybe the Persian Gulf is supplied by greater rivers and is thus less saline than the Red Sea.