The thing that is "on its last leg" is about to break down for good. The car is in poor condition and won't last much longer.

The expression actually uses a plural: "on its last legs". Imagine as though it had a stockpile of legs which it was using up, and now has only the two remaining legs. After those last two legs are used, it won't run anymore. "On its last leg" (singular) has a positive meaning, ie. a "leg" is a section of a race, and you are running the last section. The finish line is near, and the end will be a good thing. We would not actually use this phrasing, but instead: "on it's final leg". Funny how one letter can change the whole meaning!

Don't you have a dictionary?

To be "on your last leg" is to be near the end; near collapse. You have scarce resources left to complete something. "Our old family dog is on her last leg (meaning tired, near death). The "leg" here can be interpreted in two ways. First, comparing a leg to the tired or injured legs of a person or an animal after extended effort; there is not much left to stand on. A "leg" is also a counting word for a segment of a long journey. "I would be glad to sell you my car, but I must tell you that it is on its last leg." on your last legs | on its last legs Informal Meaning: If you say you're on your last legs, it can mean you're close to exhaustion, or it can mean you're close to death. If a thing is on its last legs, it's close to breaking or wearing out. For example: Bobby looks like he's on his last legs. Do you think he can make it to the top of the mountain? My old printer is on its last legs. It's time I got a new one. If you are on your last legs, you are in a very weak condition or about to die.Meaning : If you say you're on your last legs, it can mean you're close to exhaustion, or it can mean you're close to death. If a thing is on its last legs, it's close to breaking or wearing out المعنى من المصطلح : في مراحلها الآخيرة Example-:Samir looks like he's on his last legs. Do you think he can make it to the top of the mountain?x

@ Eliot. First off, last time I checked, dictionaries don't have idiomatic phrases in them. Secondly, if you don't have a helpful suggestion, why are you wasting your time tearing down other people. This is the second time that I have read an unnecessary negative answer from you.