Plain English Meaning
Your own personal rules about when you will and will not fly. They are stricter than what the law allows, because legal does not always mean safe for you on a given day.
Full Definition
A self-imposed set of weather, flight, and proficiency limits that a pilot establishes for themselves, set more conservatively than the legal minimums in the regulations. They define the conditions under which the pilot is willing to fly based on their own experience, recency, and comfort level.
Context Anchor
Used during preflight planning and weather decision-making, especially when deciding whether conditions are within your ability for that flight.
Derivation
Personal means belonging to the individual pilot. Minimums means the lowest acceptable limits — the floor below which you will not go. Together: the lowest conditions you personally , even if the regulations would let you go lower.