"Mesh" has become something of an abused term and has now been so mangled by the marketing departments that it is virtually meaningless.
Any Wi-Fi solution that cannot be delivered using a single hotspot has to be delivered using multiple hotspots creating a "cellular" coverage pattern. It could be argued that any cellular coverage pattern is a "mesh" system. "Mesh" is not some woo woo that magically somehow "does Wi-Fi better" than other systems, it's just a fleet of multiple Wi-Fi hotspots (even if it is as few as just two) just like any other Wi-Fi system with multiple hotspots.
The "trick" with multiple hotspots is hot one establishes the "backhaul" link between devices facilitating each hotspot and the rest of the (wired) network. Best backhaul is achieved using "proper" wired ethernet. Next best is probably Powerline/HomePlug technology, though it's fickle had highly dependent on how good the signalling conditions on you mains electricity circuit is. It used to be that least good backhaul is to also use Wi-Fi. However, now that Wi-Fi is getting faster it can be argued that Wi-Fi backhaul can do pretty well compared to powerline. Though cabled ethernet still beats both hands down if "speed" is your thing.
All Wi-Fi is is facilitated by devices called "Access Points" (AP's.) There's an AP built in to a SOHO Router, Repeater, Homeplug, Mesh node, "Disc," Mi-Fi, Q-Box and anything else that "does Wi-Fi." Whilst the feature set between one AP and another can vary greatly, the fundamentals of how they work at a basic level is the same - an AP is and AP is an AP, whatever it might be built in to; they all transmit the same "kind" of radio energy. For the SOHO use case, what basically differentiates all of these devices from each other is how they achieve their backhaul links as discussed above.
Just to muddy the waters even more, some "mesh" systems can use wired backhauls, some cannot, some have separate radios for the backhaul and client access signalling (often called "tri band") some do not and so on. A lot of them offer some features that used to be the preserve of enterprise systems whereby the nodes "talk" to each other to do useful stuff like automatically establish the radio channel plan, pre-stage some of the roaming hand-off and share information about which AP can "hear" each client the best in order to try and "steer" clients towards use the "best" AP and a management platform (often an "app".) But this is by no means universal.
As a buyer, one cannot assume anything about a so-called "mesh" system - it's up to us to check the specification forensically.
I think about the best thing we can say is that they are designed to easily automate setting up a multi-hotspot cellular coverage pattern where people cannot or don't want the hassle of installing proper cabled backhaul links or use powerline type technology.
For those "mesh" systems that can use Wi-Fi for the backhauls, they are essentially the same as Wi-Fi "Repeaters" albeit with some extra bells and whistles for client steering (probably.) But just like Wi-FI Repeaters, if you are going to deploy nodes that use Wi-Fi backhaul, some care is required in their physical positioning as the mesh nodes need to be "in range" of a good signal from each other as well as the area they are meant to provide client coverage for. (Of course, cabled/powerline backhaul does not suffer this issue.)
"Mesh" has it's place (like all these technologies,) but they are not silver bullets.