The Ideal Customer Profile (ICP) is not "everyone" — it's a precise description of the customer who fits you best. In B2B it's usually defined by company type (industry, revenue, headcount), their problem, and the decision-maker (the executive or owner's role).
The ICP decides everything: the offer, the channel, the creative, and even the lead-quality criteria are all built for this profile. When the ICP is vague, the marketing budget gets sprayed across the wrong people.
ICP vs a plain "target audience"
A target audience can be broad ("entrepreneurs aged 25-45"). An ICP is narrow and specific: "an IT company in a growth stage, over $100,000 in monthly revenue, with no marketing team yet." That precision is exactly what cuts cheap, low-quality leads out of your advertising.
In practice you should write the ICP down: who, in what industry, with what problem, within what budget. That document becomes the yardstick for every marketing decision that follows.