Trough and ridge are

In meteorology, a trough and a ridge are defined by their pressure characteristics and shapes. A trough is an elongated region of relatively low atmospheric pressure [2]. It is often associated with cyclonic wind shifts and unstable weather conditions, such as cloud formation and thunderstorms [5]. Conversely, a ridge is an elongated area of relatively high pressure that extends from a high-pressure center. Ridges are typically associated with anticyclonic wind shifts and stable, dry weather conditions because the air within them descends and warms, inhibiting cloud formation [1]. While closed loops define low or high-pressure cells (cyclones and anticyclones), troughs and ridges represent the extended, non-closed arms of these systems [5]. Therefore, a trough is an elongated area of low pressure, and a ridge is an elongated area of high pressure.

Sources

1. [2] https://ocean.weather.gov/product_description/keyterm.php
2. [1] https://en.wikipedia.org/wiki/Trough_(meteorology)
3. [3] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 27: Jet streams > Explanation > p. 391
4. [5] https://forecast.weather.gov/glossary.php?word=trough