he has everything a guy COULD want.

[ridskf]

what does could mean grammatically?
thank you in advance.

[marmoset]

*just an assistant ESL teacher

"'Could' is used to talk about theoretical possibility and is similar in meaning to 'might'.

• It could rain later. Take an umbrella.
• He could be there by now.
• Could he be any happier?
• It could be Sarah's. "

from: English Grammar Lessons

So, he has everything a guy might want. It is hard to buy this guy a good present.

[probus]

Without changing the meaning you could say "He has everything a guy could possibly want." In other words, it is impossible to want more than he has. He couldn't want more.