Do security groups block outbound traffic by default unless there is a corresponding inbound rule for the traffic?

Do security groups block outbound traffic by default unless there is a corresponding inbound rule for the traffic?

In other words, without a inbound rule for port 80 will outbound traffic on port 80 be allowed.   let's say the traffic outbound is originating inside the network hence there is no inbound traffic for port 80.

If there is UDP traffic on port 80 inbound then traffic on port 80 outbound will be blocked if there is no outbound rule on port 80?,... since UDP is a connectionless traffic.

dsk