A large, long-established company with reliable earnings and, usually, a steady dividend. On the PSE this is roughly the PSEi 30: the major banks, conglomerates, property developers and utilities. They are not safe in the sense of never falling, and several have had long flat stretches. What they offer is that the business is unlikely to disappear and the stock trades in enough volume that you can sell a real position without moving the price.
See also
See every term in the full PSE investing glossary.