Most Common Values (MCV list)
Also called: MCV list, most_common_vals
When PostgreSQL studies a column with ANALYZE, it records a short list of the values that appear most often, together with how frequent each one is. That is the Most Common Values (MCV) list.
What this means
When ANALYZE studies a column, it writes down the handful of values that show up most often, along with how frequent each one is. That's the MCV list. If the value in your WHERE clause is on it, the planner knows its frequency exactly and estimates perfectly, the common values are handled by name instead of by guess.
Why it matters operationally
The planner uses the MCV list to estimate how many rows a WHERE col = ... filter will match. If your value is on the list, the estimate is exact. If a hot value is missing because the list is too short, the planner guesses badly and can choose a slow plan. Raising the statistics target makes the list longer.