The load factor is the ratio between the number of stored entries and the number of buckets. A table with 6 entries across 8 buckets sits at 0.75. It is a single number describing how crowded the table is.
Why care? As the load factor rises, more keys share buckets, so collisions and chain lengths grow. Lookups that were near constant start scanning longer chains. Implementations watch this number and resize once it crosses a set threshold.
A low load factor wastes memory on empty buckets. A high one wastes time on collisions. The whole point is to keep it in a healthy middle band so average operations stay near O(1).
Rewriting in plainer words…
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