Plene (or full) spelling is the opposite of defective spelling. Note the difference between a holem-vav as here:
יוֹשֵב
and a simple holem as here:
יֹשֵב
The first word is plene spelling since the vav is preserved as part of the vowel. The second is defective. The meaning of the word is not affected. See the glossary in KHW p373 or Gesenius §8i or video