What's the AmE and BrE for "tartaruga"?

In Italian the term "tartaruga" (turtle) is used also to refer to well defined abdominal muscles on the notion that they look like a turtle shell:

Is there a slang/colloquial term or short phrase to refer to "defined addominal muscles" in AmE or BrE?

You can say that somebody has a six pack.

informal - A man’s set of visibly well-developed abdominal muscles.

Or perhaps even an eight pack.

You can also say that someone has washboard abs or a washboard stomach, although commentators on this answer suggest that this is used more in fitness circles to describe a flatter, less "ripped" set of abs than those in your picture:

[AS MODIFIER] Denoting a man’s stomach that is lean and has well-defined muscles:

Try ripped abs

MW

having high muscle definition

You could also say: shredded abs.

shredded — ODO

2 informal Having well-defined or well-developed muscles; muscular

Example:

a step-by-step plan that will help you achieve shredded abs in as little as 76 workouts