This document discusses Spanish stem-changing verbs, which are verbs that change their stem vowel sound in certain conjugations. It provides examples of four types of stem changes: e to ie, o to ue, e to i, and u to ue. Some example verbs listed are empezar, almorzar, pedir, and jugar, which follow the stem change patterns of e to ie, o to ue, e to i, and u to ue respectively in different conjugations.