der Slip
briefs / panties
Short, tight-fitting underwear without legs, worn by women, men, or children.
Für den Sport trägt er am liebsten einen bequemen Slip aus Baumwolle.
For sports, he prefers to wear comfortable cotton briefs.

briefs / panties
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briefs / panties
Short, tight-fitting underwear without legs, worn by women, men, or children.
Für den Sport trägt er am liebsten einen bequemen Slip aus Baumwolle.
For sports, he prefers to wear comfortable cotton briefs.

'Der Slip' (briefs/panties) is a loanword from English. Such words are called Anglicisms and are very common in German, especially in fashion and technology.
Im Deutschen gibt es viele Anglizismen wie „Computer“, „Hobby“ oder eben „Slip“.
In German, there are many Anglicisms such as 'Computer' (computer), 'Hobby' (hobby), or simply 'Slip' (briefs/panties).
In German, 'der Slip' (briefs/panties) refers exclusively to short, tight underwear. The English word 'slip' can also mean an underdress worn by women. The German word does not have this meaning.
Sie packte drei Slips für die Reise ein.
She packed three pairs of panties for the trip.
'Slip' (briefs/panties) is often combined with the material it is made of. Typical phrases are 'ein Slip aus Baumwolle' (cotton briefs/panties), 'aus Seide' (made of silk), or 'aus Spitze' (made of lace).
Für besondere Anlässe trägt sie gerne einen Slip aus Spitze.
For special occasions, she likes to wear lace panties.
boxer
'der Boxer' and 'der Slip' can both refer to underwear, but they do not mean the same style. 'Boxer' colloquially means a pair of boxer shorts, that is, looser underpants, usually with legs. 'Slip' means short, tight-fitting underpants without legs and can be worn by women, men, or children. The words can be confused because both belong to the category of underwear. So the important point is the shape: boxers are looser, while slips fit tightly.

Für das enge Kleid wählt Maria einen glatten Slip.
For the tight dress, Maria chooses a smooth pair of panties.
Im Laden kauft Ali neue Boxer, weil er weite Unterwäsche bequemer findet.
At the store, Ali buys new boxers because he finds loose underwear more comfortable.