der Einfluss
influence
The effect or power that a person, thing, or situation has on another.
Die Medien haben einen großen Einfluss auf die öffentliche Meinung.
The media have a major influence on public opinion.

influence
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influence
The effect or power that a person, thing, or situation has on another.
Die Medien haben einen großen Einfluss auf die öffentliche Meinung.
The media have a major influence on public opinion.

The word is made up of 'ein' (in/into) and 'Fluss' (flow/river). The idea is that something 'flows into' a situation or person and changes them as a result.
Die Entscheidung des Chefs hatte einen großen Einfluss auf die Stimmung im Team.
The boss's decision had a major influence on the mood in the team.
'Einfluss' (influence) is almost always used with the preposition 'auf' (on) and the accusative. You have or exert influence ON someone or something.
Seine Worte hatten keinen Einfluss auf meine Entscheidung.
His words had no influence on my decision.
To describe the strength or type of effect, 'Einfluss' (influence) is often combined with adjectives like 'groß' (large/major), 'stark' (strong), 'gering' (slight), 'positiv' (positive), or 'negativ' (negative).
Das Wetter hat einen starken Einfluss auf meine Laune.
The weather has a strong influence on my mood.
The phrase 'Einfluss nehmen auf' (to exert influence on) describes an active action. It means that someone is consciously trying to change or guide something or someone.
Als Elternteil möchte man positiv auf seine Kinder Einfluss nehmen.
As a parent, you want to exert a positive influence on your children.
When 'Einfluss' (influence) is used with the indefinite article ('ein') and an evaluative adjective ('gut' (good), 'schlecht' (bad)) to describe a person or group, that person or group is itself the source of the effect.
Er ist ein wirklich guter Einfluss für die ganze Mannschaft.
He is a really good influence on the whole team.
meaning / importance
'die Bedeutung' and 'der Einfluss' can both describe that something is important and affects a situation. 'Bedeutung' more often says what status something has or how important it is. 'Einfluss' more strongly says that something has an effect on another person, decision, or development. They can be confused because something of great importance often also has influence. As a practical rule: if you are asking how important something is, 'Bedeutung' fits. If you are asking what something changes or causes, 'Einfluss' fits.

Das Wetter hatte großen Einfluss auf unsere Reisepläne.
The weather had a major influence on our travel plans.
Die Bedeutung dieses Gesprächs wurde mir erst später klar.
The importance of this conversation only became clear to me later.