der Biss
bite
The action of gripping with the teeth or biting into something.
Der Biss des Hundes in den Stock war sehr kräftig.
The dog's bite into the stick was very strong.

bite
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bite
The action of gripping with the teeth or biting into something.
Der Biss des Hundes in den Stock war sehr kräftig.
The dog's bite into the stick was very strong.

'Der Biss' (bite) is the noun that belongs to the strong verb 'beißen' (to bite). This connection between verb and noun with a vowel change is common in German.
Pass auf den Hund auf, er beißt manchmal.
Watch out for the dog; he sometimes bites.
A 'Biss' (bite) refers to a wound caused by teeth or jaws (e.g. 'Hundebiss' (dog bite)). A wound caused by a stinger or proboscis (e.g. from a bee or mosquito), on the other hand, is called 'Stich' (sting/bite).
Der Schlangenbiss war zum Glück nicht giftig.
Fortunately, the snakebite was not poisonous.
In colloquial language, the phrase 'einen Biss nehmen' (to take a bite) or 'einen Biss probieren' (to try a bite) is used when asking someone if you may taste a small piece of their food.
Dein Kuchen sieht lecker aus, darf ich mal einen Biss probieren?
Your cake looks delicious; can I try a bite?
In a figurative sense, 'Biss' (bite) means something like assertiveness or energy. Typical phrases are 'Biss haben' (to have drive), 'Biss zeigen' (to show drive), or 'der Biss fehlt' (the drive is missing), often in the context of sports or work.
Der Mannschaft fehlte heute der Biss, um das Spiel zu gewinnen.
The team lacked the drive today to win the game.
sting / stitch
'Stich' and 'Biss' can both describe a small injury or irritation of the skin, especially with animals or insects. The most important difference is what causes it. A 'Stich' comes from something pointed, for example a needle or an insect stinger. A 'Biss' actually comes from teeth, for example with a dog. In everyday language, people sometimes also say 'Biss' for insects if the skin itches or turns red afterward. That is why the words can be confusing. More precisely: mosquitoes and bees sting; dogs and cats bite.

Der Biss des Hundes musste sofort von einer Ärztin untersucht werden.
The dog bite had to be examined by a doctor right away.
Nach dem Spaziergang juckt der Stich an meinem Arm sehr.
After the walk, the sting on my arm itches a lot.