Accuracy of pitch in playing or singing, or on a stringed instrument such as a guitar. In guitar terms, it’s how well the guitar stays in tune along the whole length of the neck. Excellent intonation would be if you played a note on each fret (1-12) on each string and every note was in tune.
The distance between the fingerboard and the string. This determines how easy it is to sound notes when you press down on the strings. Typically, you want lower action. Beginner guitars are notorious for having action that is much too high, which is why it’s important to find brands that consistently make guitars with proper string height.