A meaning gap is an available position in the meaning landscape of a market: a desirable meaning that connects with user desires but that no existing product currently occupies. Meaning gaps are the raw material of initial advantages.
In a saturated market, the intuition is that there is no room. Every feature has been built. Every position has been taken. The only option is to compete on execution and price. This intuition is thinking in functional terms. Functionally, a market may be saturated. Symbolically, it almost never is.
The water market had Evian, Fiji, Voss, Smartwater, and approximately infinite private labels at every price point. Functionally exhausted. But no product meant "the water for people who find wellness culture absurd." That position was empty. Liquid Death filled it and generated $263 million in revenue.
The team communication market had email, IRC, Skype, and HipChat. Functionally saturated. But no product meant "email killer; organized, fast internal communication without the formality of email and without the stigma of chat." Slack filled it.
Finding a meaning gap requires looking at the market through the lens of the user fantasy frame: what do users in this category desire, identify with, resent, and believe; and which of those is currently being addressed by no product's meaning? The gap is there. The question is whether you have the boldness to fill it.
See also: User Fantasy Frame, Boldness as Prerequisite, Winning in a Saturated Market.