die Bedingung
requirement
A prerequisite that must be fulfilled so that something else can happen or be valid.
Pünktlichkeit ist eine wichtige Bedingung für diese Arbeitsstelle.
Punctuality is an important requirement for this job.

condition / requirement
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requirement
A prerequisite that must be fulfilled so that something else can happen or be valid.
Pünktlichkeit ist eine wichtige Bedingung für diese Arbeitsstelle.
Punctuality is an important requirement for this job.

'Die Bedingung' means 'prerequisite' or 'requirement'. It is often confused with the English word 'condition', which can also describe the physical state of something. For physical state, German uses 'der Zustand' (condition/state).
Das Auto ist in einem sehr guten Zustand.
The car is in very good condition.
'Die Bedingung' (condition/requirement) is related to the adverb 'unbedingt' (absolutely, definitely). 'Unbedingt' literally means 'without condition' and expresses that something is absolutely necessary.
Du musst dir diesen Film unbedingt ansehen!
You absolutely have to watch this film!
In the sense of a prerequisite, 'Bedingung' (requirement/condition) is often used with the verbs 'stellen' (to set/make) and 'erfüllen' (to fulfill/meet). Someone can 'eine Bedingung stellen' (set a condition), and the other side must 'diese Bedingung erfüllen' (meet this condition).
Der Verkäufer stellte die Bedingung, dass der Preis sofort bezahlt wird.
The seller set the condition that the price be paid immediately.
When general circumstances or conditions are being discussed, the plural form 'die Bedingungen' is almost always used. Typical examples are 'Arbeitsbedingungen' (working conditions), 'Lebensbedingungen' (living conditions), or 'Wetterbedingungen' (weather conditions).
Die Sportler klagten über die extremen Wetterbedingungen.
The athletes complained about the extreme weather conditions.
The fixed expression 'unter der Bedingung, dass' (on the condition that) introduces a conditional clause. The following part of the sentence is a subordinate clause, in which the conjugated verb stands at the end.
Ich leihe dir mein Auto, unter der Bedingung, dass du es volltankst.
I'll lend you my car on the condition that you fill up the tank.
basis / foundation
'die Grundlage' and 'die Bedingung' can both describe something that is important for something else. The difference lies in the perspective. A 'Grundlage' is the basis or foundation on which something is built, for example knowledge, trust, or data. A 'Bedingung' is something that must be fulfilled so that something may happen or is possible. They can be confused because both are often mentioned before a decision or action. If you want to say what something is based on, use 'Grundlage'. If you want to say what must be fulfilled first, use 'Bedingung'.

Er bekommt den freien Tag unter der Bedingung, dass er die Arbeit vorher fertig macht.
He gets the day off on the condition that he finishes the work beforehand.
Gute Deutschkenntnisse sind eine wichtige Grundlage für den Kurs.
Good German skills are an important foundation for the course.