Maxperson
Morkus from Orkus
Or you can say, "I think back to the things I learned of giants in my youth and try to recall what this might be." which would prompt the DM to probably ask for a lore check of some kind."In the clearing ahead, you see a pair of 9' tall humanlike figures. They seem very thin and have minor deformities- one has an obvious club foot, and the other's face looks like it's partially melted due to a malformed jaw. They wear furs and hides with pieces of metal armor stitched into strategic places, and wield spears."
From this description, how does one tell, exactly, if they are dealing with an easily dealt with threat, or a deadly encounter? You can metagame that the DM isn't going to use an encounter of two easily defeated mooks, but you really don't know. Are they as tough as giants? Trolls? Ogres? Bugbears?
No idea. Should you alpha strike by using a powerful spell, or attempt to use minimal resources? No amount of experience can let you make an informed decision, unless you know exactly what these things are from player experience.
Or again, you could metagame and think "well, this is the second encounter, we might face up to 6 more today. Or not."
Now, I could say, "this is a Verbeeg, it's slightly more dangerous than an Ogre." And maybe that's enough.
Or I could say "he has 5 hit dice, one attack, and a Strength of about 20 and a (surprisingly good, based on the description) 16 AC." Now, I know the players can make a proper tactical assessment.
Or you can say(because of the background you wrote and turned in), "My village bordered the Megalith Mountains, where many clans of giants lived. We dealt with giants on a regular basis." Prompting the DM to give you a roll of some sort, or just tell you what it is since you've probably seen one before.
That's what prior experience and lore rolls are for.D&D is a game where a little bunny rabbit can actually be a horrible abomination. Description doesn't actually tell the player very much about what they are dealing with. There are, however, cues a trained combatant can glean from someone's stance, how they carry their weapons, the condition of said weapons, and a hundred more intangibles that I don't have the time to describe (or think about in the moment).
Some feel that you should have to have a special feature, like the Battlemaster, to be able to size up foes. I'm in the opposite camp- everyone should be able to do this if they're in the business of facing down deadly foes on a daily basis.
There's no need to for the only options to be to metagame or act without any knowledge of what it might be at all.