I'm gonna be honest, I have no idea what the word meta means. I've just heard other people say it and assumed what it meant
The easiest way to remember the meaning is "Most Effective Tactic Available", and while it can have multiple meanings, when speaking of meta in a Splatoon sense it's the most effective tactics, weapons and builds in terms of effectiveness, win-rate, et cetera. In other words, it's a way of saying "the current state of things". Meta describes which weapons / combinations (and gear builds) of such in a squad (and strategies) have proved most viable to achieve a win. Certain weapons, like the Splattershot, are considered a constant part of the Splatoon "meta" because they're powerful and can fill multiple roles, whereas other weapons are less favored in the "meta" because they're easily countered and little maps favor them.
So taking the charger for example, little maps cater to them specifically, quite a few maps give them little excellent angles and positions to work with and due to the openness of most maps, they don't have any designated perches where they can safely snipe from anymore and with the current state of lots of short-mid range shooters being able to flank them with ease and chargers having little to defend themselves when someone enters close-combat range, they're not considered as "safe" to pick as weapons who fare better in multiple scenarios and don't die whenever someone flanks them. Personally, I think the Splat Charger series (arguably Squiffer and Bambi) can have a place in the meta since they have good kits to work with. Not on all maps though and they need a proper team to work their magic and to add to the misery, they need to be way more mobile than they used to in Splatoon 1.
(If you used to be a mobile turfy sniper back in S1, that change won't kick you as hard as others) The E-Liter is in a terrible place right now compared to his cousins though, so unless you really know what you're doing, you should opt for the lighter options instead.
Again, I'm not going to tell you what to do with that information. If you want to master the Charger, more power to you. Just wanted to warn you that it's a tad harder to pull through right now, especially if you're mostly playing Solo. It's perfectly doable, the Charger is still a pretty good weapon, but you need to put in much more work to be as efficient as other weapons that are considered meta right now, so it's up to you if you want to put in the extra work. The threads I linked you give you excellent advice on where to improve on, if you're still in the dark on some things after reading them you can ask anytime, though.