der Spruch
saying
A short, memorable sentence that contains a piece of life wisdom, a motto, or a joke; a proverb or idiom.
An der Wand hing ein Schild mit dem Spruch: „Carpe Diem“.
On the wall hung a sign with the saying: 'Carpe Diem.'

saying / remark / ruling
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saying
A short, memorable sentence that contains a piece of life wisdom, a motto, or a joke; a proverb or idiom.
An der Wand hing ein Schild mit dem Spruch: „Carpe Diem“.
On the wall hung a sign with the saying: 'Carpe Diem.'

'Der Spruch' (saying/remark/ruling) belongs to the word family of 'sprechen' (to speak). A 'Spruch' is therefore something that is said or 'spoken' and often has a special, memorable form.
Kennst du den Spruch „Wer rastet, der rostet“?
Do you know the saying 'Wer rastet, der rostet' (you snooze, you lose / if you rest, you rust)?
The meaning can often be recognized from context. If it is about wisdom or sayings, meaning 1 is intended. In connection with negative adjectives like 'dumm' (stupid) or 'frech' (cheeky), it is meaning 2. In a legal context (court, judgment), it is meaning 3.
Mein Opa kennt viele alte Sprüche.
My grandpa knows many old sayings.
In the colloquial sense of a cheeky remark, there are the fixed expressions 'Sprüche machen' and 'Sprüche klopfen'. Both mean that someone is constantly making funny or inappropriate comments.
Hör auf, immer so dumme Sprüche zu klopfen!
Stop always making such stupid remarks!
The meaning 'Urteil' (judgment) or 'Entscheidung' (decision) is limited to legal language. In everyday speech, 'der Spruch' is never used in this sense.
Nach langer Beratung verkündete der Richter den Spruch.
After lengthy deliberation, the judge announced the ruling.
decision
'die Entscheidung' and 'der Spruch' can both mean an official outcome in a legal context. 'Entscheidung' is the normal, broad word for a decision or ruling, including by authorities or courts. 'Spruch' in this meaning belongs to legal language and sounds much more specific. In everyday language, 'Spruch' usually means something else, for example a short saying, a motto, or a cheeky remark. That is why the words can be confused if you only know 'Spruch' from everyday language. For normal situations, 'Entscheidung' is almost always a better fit.

Nach langer Beratung verkündete das Schiedsgericht seinen Spruch.
After a long deliberation, the arbitration court announced its ruling.
Die Entscheidung des Gerichts wird am Freitag bekannt gegeben.
The court's ruling will be announced on Friday.