die Kondition
fitness
A person's physical condition and endurance, especially in relation to athletic performance.
Durch regelmäßiges Joggen hat er seine Kondition deutlich verbessert.
Through regular jogging, he significantly improved his fitness.

fitness / terms
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fitness
A person's physical condition and endurance, especially in relation to athletic performance.
Durch regelmäßiges Joggen hat er seine Kondition deutlich verbessert.
Through regular jogging, he significantly improved his fitness.

Careful: 'die Kondition' (fitness) does not mean the same as the English 'condition'. 'Kondition' in the singular almost always means physical fitness. The general condition of a person is 'der Zustand' (condition/state) or 'die Verfassung' (condition/state).
Der Arzt fragte: „Wie ist der allgemeine Zustand des Patienten?“
The doctor asked, 'What is the patient's general condition?'
The meaning can almost always be recognized from the number (singular/plural). 'Die Kondition' (singular) refers to physical endurance. 'Die Konditionen' (plural) refers to the terms of a contract or business deal.
Er hat eine sehr gute Kondition und läuft jeden Tag zehn Kilometer.
He has very good fitness and runs ten kilometers every day.
In a sports context, 'Kondition' (fitness) is often combined with verbs like 'haben' (to have), 'trainieren' (to train), 'verbessern' (to improve), or 'aufbauen' (to build up). You can have 'gute Kondition' (good fitness) or 'schlechte Kondition' (poor fitness).
Ich muss dringend meine Kondition trainieren, ich bin schnell außer Atem.
I urgently need to work on my fitness; I get out of breath quickly.
In a business context, people talk about 'faire' (fair), 'günstige' (favorable), or 'schlechte' (bad) 'Konditionen' (terms). Verbs often used here include 'aushandeln' (to negotiate), 'anbieten' (to offer), or 'akzeptieren' (to accept).
Die Bank bietet Kredite zu sehr günstigen Konditionen an.
The bank offers loans on very favorable terms.
form / shape
'die Form' and 'die Kondition' can both say how physically capable someone is. 'in Form sein' (to be in shape) means generally that someone is fit and can perform well. 'die Kondition' refers especially to physical endurance, meaning how long someone can run, train, or exert themselves. Learners may confuse the words because both occur in sports. 'Form' is broader and can also mean someone's general condition. 'Kondition' is more precise when it is about endurance and training.

Beim Wandern merkt Paul, dass seine Kondition besser geworden ist.
While hiking, Paul notices that his fitness has improved.
Wegen der langen Pause ist der Spieler noch nicht wieder in Form.
Because of the long break, the player is not back in shape yet.