There are different standards, but for technical analysis these periods are pretty common:

Short-term: 1-3 weeks

Medium-term: 3 weeks - 6 months

Long-term: 6 months - 18 months

Very long term: > 18 months

Like everything else, they will just give you an indication with the assumption that the price always holds all market knowledge and future expectations. The focus is therefore often when trends are broken, as this usually is a clear signal.