Primary attributes are stats that influence most aspects of gameplay: Examples: strength, vitality, dexterity,magic.
They are typically upgraded with level-up points or from specific consumables. Secondary attributes are usually derived from primaries and item/skill effects.
Alternative systems replace primary attributes with character level(adding class specific bonus scaled by by level(essentially fixed hidden primary attributes)) or skill-leveling by use system(where skill level/stats are upgraded by use, but character level is absent)