Waste thoughts are those that don't contribute to your goals, well-being, or present moment focus. They can include rumination, negative self-talk, or dwelling on things beyond your control. "waste thoughts" refer to unnecessary or distracting thoughts that are unproductive and can drain energy, often stemming from dwelling on the past or worrying about the future. 

Thinking about past mistakes or regrets. Worrying excessively about future outcomes. Being distracted by unimportant information or advertisements. Having random, intrusive thoughts that don't serve a purpose, thinking of others, comparing with others  and so on.Wasteful thoughts as the name suggests are a total waste of time. When we take time and do not use it properly, we are actually abusing it. This may sound a little dramatic but just think about it for a minute.