Definition of polarised
When we speak of polarised its range, we mean a range divided into two parts, a very strong part and a weaker part. Concretely, it can take several forms. For example, you want to have a polarized 3bet of the small blind? So you have a polarized range made of very strong hands like AA, KK, QQ and AKs, but also of weaker hands that are played well, like 56s, 67s, 78s, etc. We can also talk about a polarized range of check-raise. For example, if you decide to check-raiser polarized on a flop, on a flop like A-7-8 with 2 spades, you could make a check-raise with a very strong hand like 77 or with a straight or flush draw.
What are the advantages of a polarized range?
The question can be asked. Good players have games that they make in a polarized way. Let's take an extreme example to understand each other. You bluff 100% of the time on the river. Obviously, your opponents will eventually realize this and in a short time, your bluffs will no longer be successful. Now, imagine that every time you're all in on the river, you have the nuts. In no time at all, no one will call your bets on the river. Now, if you have a polarized range on the river and you are 50% of the time in value and 50% of the time in bluff, it becomes much harder for your opponents to read you!