Zoning codes usually say, district by district, which uses are permitted, which need a hearing and which are not allowed, often in a use table. A use marked as permitted is allowed by right. The owner does not need anyone's permission to choose that use, only to show that the project meets the rules.
By right does not mean no review. The project still has to meet the district's dimensional standards, such as setbacks, height, lot size and parking, and it still needs the usual permits, which may include site plan review, stormwater and tree review, and a building permit. What it does not need is a discretionary decision, so neighbors cannot vote it down if the plans comply.
That certainty is why by-right capacity matters so much to land value. A site's by-right yield is what can be built with the least risk and time; anything more usually depends on a rezoning, a special exception, a variance or a bonus program, each with its own odds and timeline.
Codes mark uses in different ways, with letters such as P for permitted, C for conditional and S for special exception, and the meaning of each mark is defined in the code itself. In Charleston County, South Carolina, for example, a single-family detached house is permitted by right in many residential districts, while other housing types in the same district need a hearing.