Question: is a specific time point in a wave’s cycle

title: Phase (waves)
text: Time is sometimes used ( instead of angle ) to express position within the cycle of an oscillation . A phase difference is analogous to two athletes running around a race track at the same speed and direction but starting at different positions on the track . They pass a point at different instants in time . But the time difference ( phase difference ) between them is a constant - same for every pass since they are at the same speed and in the same direction . If they were at different speeds ( different frequencies ) , the phase difference is undefined and would only reflect different starting positions . Technically , phase difference between two entities at various frequencies is undefined and does not exist .