taggen
to tag
On social media or digital platforms, to mark a person in a photo or post, or to label content with a keyword.
Ich habe dich auf dem Gruppenfoto von der Party getaggt.
I tagged you in the group photo from the party.

to tag
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to tag
On social media or digital platforms, to mark a person in a photo or post, or to label content with a keyword.
Ich habe dich auf dem Gruppenfoto von der Party getaggt.
I tagged you in the group photo from the party.

'Taggen' (to tag) is a loanword from English ('to tag'). In German, it is conjugated like a regular weak verb: ich tagge, du taggst, er hat getaggt.
Er hat alle seine Freunde auf dem Bild getaggt.
He tagged all his friends in the picture.
The meaning depends heavily on the context. In connection with social media, photos, and posts, it means 'markieren' (to tag/mark). In the context of graffiti, walls, and pens, it means to leave one's name or sign behind.
Kannst du mich in dem Beitrag taggen, damit ich ihn auch sehe?
Can you tag me in the post so that I can see it too?
In the digital world, 'taggen' (to tag) often follows the pattern: 'jemanden (Akkusativ) auf etwas (Dativ) taggen' (to tag someone in/on something). The 'something' is usually a photo, a picture, or a post.
Sie wurde auf einem alten Urlaubsfoto getaggt.
She was tagged in an old vacation photo.
to mention
'erwähnen' and 'taggen' can both make a person or topic visible. 'erwähnen' is used generally in conversations or texts when you briefly name something. 'taggen' is used mainly digitally, for example on social media, when you tag a person or add a keyword to a post. The words can be confused because online you sometimes mention someone and tag them at the same time. If it is only about naming or mentioning someone or something, 'erwähnen' fits. If it is about a technical marking on a platform, 'taggen' fits.

Nach dem Ausflug taggt er seine Freunde auf dem Foto.
After the trip, he tags his friends in the photo.
Die Mitarbeiterin erwähnt in der Pause, dass das Team morgen früher beginnt.
During the break, the employee mentions that the team is starting earlier tomorrow.