A "screaming seagull" can refer to two different things, depending on the context.

1. According to Urban Dictionary, a "screaming seagull" is a sexual act where a person has sex with someone on the beach, pulls out before ejaculation, sticks their penis in the sand, and then re-inserts it. This definition is vulgar and not appropriate for all audiences.

2. Seagulls are known for their loud and distinctive calls, which can be described as "screaming". Seagulls make a variety of different calls, which can indicate different things such as attracting mates, indicating danger, or indicating feeding for chicks.

In summary, a "screaming seagull" can either refer to a sexual act or to the loud calls made by seagulls.