die Senke
depression
A hollow or lower-lying area in a landscape or on a surface.
Nach dem Regen sammelte sich das Wasser in einer Senke auf dem Feld.
After the rain, water collected in a depression in the field.

depression / dip
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depression
A hollow or lower-lying area in a landscape or on a surface.
Nach dem Regen sammelte sich das Wasser in einer Senke auf dem Feld.
After the rain, water collected in a depression in the field.

The noun 'die Senke' (depression/dip) is closely related to the verb 'sinken' (to sink). A 'Senke' is therefore literally a place that has 'sunk' or lies lower than its surroundings.
Durch das Absinken des Grundwasserspiegels entstand eine große Senke.
The lowering of the groundwater level created a large depression.
You can easily recognize the meaning from the context. Words like 'Landschaft' (landscape), 'Feld' (field), or 'Boden' (ground/soil) point to the geographical depression. Words like 'Wirtschaft' (economy), 'Aktienkurs' (stock price), or 'Zahlen' (figures/numbers) point to the statistical low point.
In der Senke wuchsen besondere Pflanzen, die es feucht mögen.
Special plants that like moisture grew in the depression.
In a geographical context, 'Senke' (depression) is often used with the preposition 'in' (in). Typical formulations are 'in einer Senke liegen' (to lie in a depression), 'sich in einer Senke befinden' (to be located in a depression), or 'Wasser sammelt sich in der Senke' (water collects in the depression).
Das kleine Dorf liegt geschützt in einer Senke zwischen den Hügeln.
The small village lies sheltered in a depression between the hills.
increase / rise
'die Erhöhung' and 'die Senke' both describe shapes in terrain, but they point in opposite directions. An 'Erhöhung' is a place that is higher than its surroundings. A 'Senke' is a place that is lower than its surroundings. In a landscape, the difference is easy to remember: you go up onto an 'Erhöhung', and down into a 'Senke'.

In der Senke hinter dem Haus sammelt sich oft Wasser.
Water often collects in the dip behind the house.
Nach dem Regen war die Erhöhung auf der Wiese noch trocken.
After the rain, the rise in the meadow was still dry.