A narrow system for university admissions refers to systems which evaluate relatively few criteria. They focus on grades and standardized tests as the main evaluation criteria for candidates. Examples include the A-Levels in the UK, and the Gaokao in China.
In contrast, a holistic system aims to evaluate the entirety of a candidate's profile, and may look at background, motivation, a wider range of extracurriculars, as well as academic criteria, often through the form of personalized essays. The US is the primary example.