Marxist = A follower of Karl Marx, the inventor of Communism. Here's a simplistic explanation of communist thought. In capitalism, the wealth produced by the whole population isn't equally shared by all participants. All profit comes from inputs + means of productions. For example, when you make and sell a hamburger,

Means of production: cooking equipment, shop (lease or own).
Inputs: meat, bread etc., human work (burger flipping guy).

If you pay all this (meat, bread, rent, 5 minutes of flipper's work etc.) $3 and you sell the burger for $5, the $2 of profit are only possible because you underpay the burger flipper, who doesn't own the cooking equipment or (part of) the physical shop. So you are "stealing" from the workers, who should collectively own the shop and share the $2. Ownership of the burger enterprise (the shop, pans, cooking equipment, meat and bread orders etc.) should be distributed among the workers.

In practice, collective ownership turns into a nightmare where the big political bosses own everything and the burger flipping plebs own nothing. No one is motivated to open burger shops. It may be illegal to open your business, even. The economy stagnates, poverty spreads.

TL;DR Some people get richer than others because they own the means of production (factories) and pay the workers less than fairly.

Maxi = Bitcoin maximalist. Here's a simplistic explanation of bitcoin maximalism. There's bitcoin and there are shitcoins. The latter are very different from bitcoin. Bitcoin is good, shitcoins are bad.

TL;DR Shitcoins are shit.

Examples:  JJG and many others here.

In practice, Maxis and Marxists are distinct groups. Very few maxis are marxists. Very few marxists are maxis. Maxis are usually capitalist at their core, often with an anarcho-capitalist tinge. Especially old school maxis, such as the people you can find in tthis little club.

I hope this helps.