tagsüber
during the day
During the daytime; in the period between sunrise and sunset, as opposed to the night.
Tagsüber ist es hier sehr laut, aber nachts ist es ruhig.
During the day it is very loud here, but at night it is quiet.

during the day
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during the day
During the daytime; in the period between sunrise and sunset, as opposed to the night.
Tagsüber ist es hier sehr laut, aber nachts ist es ruhig.
During the day it is very loud here, but at night it is quiet.

The word is made up of 'Tag' (day), the linking -s, and 'über' (over). So it literally means 'spread over the day'.
Tagsüber arbeite ich im Büro, abends entspanne ich mich zu Hause.
During the day I work in the office; in the evening I relax at home.
As an adverb, 'tagsüber' (during the day) can stand at the beginning of the sentence (position 1) or in the middle of the sentence. If it stands at the beginning, the verb follows immediately.
Tagsüber scheint die Sonne.
During the day, the sun shines.
'Tagsüber' (during the day) is very often used as a direct contrast to 'nachts' (at night), to distinguish activities or states during the day from those at night.
Viele Tiere sind tagsüber aktiv und schlafen nachts.
Many animals are active during the day and sleep at night.
daily
'täglich' and 'tagsüber' both have to do with time, but they answer different questions. 'täglich' says how often something happens: every day. 'tagsüber' says when during the day something happens: during the daytime and not at night. They can be confused because both contain the word 'Tag' (day). If you mean repetition, use 'täglich'. If you mean the period between morning and evening, use 'tagsüber'.

Tagsüber ist die Straße laut, aber nachts wird es ruhig.
During the day, the street is loud, but at night it becomes quiet.
Sie prüft im Büro täglich ihre E-Mails.
She checks her emails at the office every day.