die Beule
bump
A swelling on the body, typically caused by a knock or blow.
Nachdem er gegen die Tür gelaufen war, hatte er eine dicke Beule an der Stirn.
After he walked into the door, he had a big bump on his forehead.

bump / dent
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bump
A swelling on the body, typically caused by a knock or blow.
Nachdem er gegen die Tür gelaufen war, hatte er eine dicke Beule an der Stirn.
After he walked into the door, he had a big bump on his forehead.

The context makes the meaning clear. If people are talking about body parts like 'Kopf' (head) or 'Stirn' (forehead), it means a swelling. If they are talking about objects like 'Auto' (car) or 'Kühlschrank' (refrigerator), it means a dent in the surface.
Das Kind ist hingefallen und hat jetzt eine Beule am Knie.
The child fell down and now has a bump on his knee.
When referring to a swelling on the body, the most common verbs are 'eine Beule haben' (to have a bump) or 'eine Beule bekommen' (to get a bump). The spot is often given with 'an' + dative.
Pass auf, sonst holst du dir noch eine Beule am Kopf!
Be careful, or you'll get a bump on your head!
When a dent in an object is meant, the construction 'eine Beule in etwas machen' (to make a dent in something) or 'in etwas fahren' (to drive into something / dent something while driving) is often used. The preposition 'in' takes the accusative here.
Der Hagel hat viele kleine Beulen in das Autodach gemacht.
The hail made lots of small dents in the car roof.
blister / bladder / bubble
'die Blase' and 'die Beule' can both refer to a visible spot on the body. The important difference is the cause and the shape. A 'Blase' is usually filled with fluid and often forms because of friction, for example on the foot. A 'Beule' is more likely to result from a knock or blow and is a firm swelling. Learners may confuse the words because both can look like a small raised area on the skin. When new shoes rub, you are more likely to say 'Blase'; after a blow to the head, you are more likely to say 'Beule'.

Tom ist gegen die Tür gelaufen und hat jetzt eine Beule an der Stirn.
Tom walked into the door and now has a bump on his forehead.
Nach der langen Wanderung hatte Lisa eine Blase an der Ferse.
After the long hike, Lisa had a blister on her heel.