I feel like these terms need to be defined so that everyone is on the same page. As I understand them:
Minmaxing:
Maxing your primary attributes/gear/abilities at the cost of minimizing things you deem non-essential to your character's primary purpose. A minmaxed character should have a 17 in their primary, a 16 in their secondary, and 8 or 9 in ~two "dump" stats (with Point Buy). They have obvious and devastating weaknesses.
Powergaming:
Related to minmaxing, but more about Being Maximally Effective Overall than Being the Best at One Thing. Such a player will choose feats/spells/multiclassing to be the most effective character and focus on using optimal tactics while in combat. They *can and often will* minmax, but it's not a prerequisite. If only some players powergame, combats will be unbalanced and the DM will likely need to compensate somehow.
Munchkining:
The more advanced form of powergamer, who makes heavy use of unintended combinations via exploits, loopholes, and vagueness in the rules. A munchkin is a powergamer, but a powergamer isn't necessarily a munchkin.
Optimizing, or "Playing an Effective & Well-Rounded Character":
Basically what @Kanisatha describes above. Your primary stat is good (16 with Point Buy), your secondary stats are okay but not necessary amazing (~12-14), and you don't necessarily have multiple dump stats.
Playing a suboptimal, but still effective, character (usually for roleplay reasons):
Similar to above, but you *slightly* decrease some of your primary/secondary stats. The focus is more on creating the believable character that you want to roleplay as. I'd argue that there's still a minimum Primary Ability Score that you can have and still be in this category: 14. Anything lower, unless you prepare by e.g., only taking buff/area control spells, and you are...
Gimping your Character: ([In Solo Play] Doing a Challenge Run, or [In Multiplayer] Being an Ineffective Teammate)
Building a character that is so unoptimized that they don't pull anywhere near their weight and actively make it harder for the team to succeed. E.g., a Wizard with an Int of 10 or less; a Frontline Fighter with <10 Con; a Monk with <10 Wis. These characters will spend most of their time doing little damage, missing, dying, or dead.
Importantly, none of the above are *necessarily exclusive* with good roleplay. Powergamers can be good roleplayers while suboptimal-character players can be That Guy, and vice versa.
What you described as "minmaxing" is sound closer to the "optimizing" description then the actual minmaxing. Minmaxing can also be, and usually, used in a wider sense, of gameplay that focused not only on maxing your attributes/gear/abilities, but also making all of your in game decisions, including whole character creation, based on the mechanical aspect of the game, with no actual attention given to the roleplay, lore and narrative, or it is build based on the mechanics. That doesn't necessarily imply that they have any "weaknesses", they could have equal number in every stat, if that make them objectively stronger overall. The weaknesses that can occur from minmaxing, its just the game rules trying to shut down that kind of behavior, but it not always works. And Powergaming implying the gameplay where player trying to get more powerful, no matter if that doesn't make sense from the story/roleplay perspective, or it is against sportsmanship towards the other players, and minmaxing as you said could be a part of powergaming, but powergaming is more abstract and wider therm. For example character who making all of his moral decisions on his powergain instead of his character morals
Imho the first three, from the top, should be strictly banned from any good dnd campaign, and, at least, not a main development focus in a video game that based on dnd, as it often happens, especially with the mmo's
