der Eintrag
entry
A single piece of information that is written or entered into a list, book, form, or database.
Der Notar prüfte den Eintrag im Grundbuch.
The notary checked the entry in the land register.

entry
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entry
A single piece of information that is written or entered into a list, book, form, or database.
Der Notar prüfte den Eintrag im Grundbuch.
The notary checked the entry in the land register.

'Der Eintrag' (the entry) is the noun corresponding to the separable verb 'eintragen' (to enter). The action is 'etwas eintragen' (to enter something), and the result of this action is 'der Eintrag' (the entry).
Bitte tragen Sie Ihren Namen in die Liste ein.
Please enter your name in the list.
In official or formal contexts, you often find combinations such as 'Eintrag im Register' (entry in the register), 'im Pass' (in the passport), or 'im Kalender' (in the calendar). Common verbs are 'einen Eintrag machen' (to make an entry), 'vornehmen' (to make/carry out), or 'löschen' (to delete).
Der Beamte hat einen neuen Eintrag in meinem Pass vorgenommen.
The official made a new entry in my passport.
When 'Eintrag' (entry/post) is mentioned in digital media, words like 'Blog' (blog), 'Forum' (forum), 'Gästebuch' (guestbook), or 'Kommentar' (comment) are often nearby. Typical verbs here are 'verfassen' (to write), 'posten' (to post), or 'kommentieren' (to comment on).
Sein kritischer Eintrag im Forum wurde schnell gelöscht.
His critical post in the forum was quickly deleted.
contribution / post
'der Beitrag' and 'der Eintrag' can both refer to a text on the internet, for example in a blog or forum. 'Beitrag' tends to sound more like a publication that someone writes or shares for others. 'Eintrag' emphasizes more that something has been entered in a particular place, for example in a list, a form, a database, or also in a blog. Online, the words can sometimes seem almost the same. When you mean a post or a content-based publication, 'Beitrag' is often more natural. When you mean a single stored piece of information or an item in a list, 'Eintrag' fits better.

Aus Versehen habe ich den Eintrag im Kalender gelöscht.
I accidentally deleted the entry in the calendar.
Die Chefin liest den neuen Beitrag im Firmenblog vor der Besprechung.
The boss reads the new post in the company blog before the meeting.