I though this question could use a tag about intonation: Guitar isn't playing in tune
The problem is that "intonation" can be used differently in other musical contexts, such as in singing. So we'd need guitar-intonation or something like that. I'm also not sure whether tuning is sufficient. Obviously tuning in general is a superset of tuning for intonation, but I'm not sure if it would be better to have a specific tag as well.