Overtraining is a physical, behavioral and emotional condition that occurs when the volume and intensity of an individual's exercise exceeds their recovery capacity
😆 sounds like a description of being tired and fatigued to me.
I may be knackered immediately after a long ride but probably fine the next day. If I'm pushing hard on my commute every day I start to feel more tired and fatigued by the end of the week, legs feel a bit dead, etc. If thats not being tired and fatigued and caused by over training then I don't know what is.