* Perceived as easy to get into: This is the most common understanding. A "safety school" is one where the applicant believes they have a very high probability of acceptance based on their academic record and other application materials. It's a backup plan in case they don't get into their preferred, more competitive schools.
* Less academically rigorous (sometimes): While not always the case, safety schools might be perceived as having less demanding academic standards than more prestigious universities. However, this is a generalization and can be inaccurate. Many excellent, high-quality colleges might be considered "safety schools" for certain applicants.
* A lower-ranked college (sometimes): Similar to the point above, a safety school might be lower ranked in national or state college rankings, but this is not a guaranteed characteristic.
In short, a "safety college" is entirely relative to the individual applicant and their academic profile. What is a safety school for one student might be a reach school for another.