rest position - the undisturbed position of particles or fields when they are not vibrating;
displacement - the distance that a certain point in the medium has moved from its rest position;
peak - the highest point above the rest position;
trough - the lowest point below the rest position;
amplitude - the maximum displacement of a point of a wave from its rest position.
wavelength - distance covered by a full cycle of the wave, usually measured from peak to peak, or trough to trough. Wavelength is measured in m.
time period T - the time taken for a full cycle of the wave, usually measured from peak to peak, or trough to trough. Period is measured in s. A period of 2 s means that the time for one complete vibration is 2 s or that the time taken for one complete wave to pass a point is 2 s.
frequency f - the number of waves passing a point each second. Frequency is measured in hertz Hz. A frequency of 50 Hz means there are 50 vibrations every second.