die Verabredung
date / meetup
A planned meeting with one or more people at a specific time and place, usually in a private context.
Ich habe heute Abend eine Verabredung mit Freunden im Kino.
I have a date with friends at the cinema this evening.

date / arrangement
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date / meetup
A planned meeting with one or more people at a specific time and place, usually in a private context.
Ich habe heute Abend eine Verabredung mit Freunden im Kino.
I have a date with friends at the cinema this evening.

'Die Verabredung' (the date/arrangement) is the noun corresponding to the reflexive verb 'sich verabreden' (to arrange to meet). When people 'sich verabreden' (arrange to meet), the result is a 'Verabredung' (date/arrangement).
Wir haben uns für Freitagabend verabredet.
We arranged to meet on Friday evening.
The word has two meanings: most often it is a countable event ('eine Verabredung' — one date/appointment, 'zwei Verabredungen' — two dates/appointments). Less commonly, it describes the abstract process of planning, which is not countable.
Ich habe heute zwei Verabredungen, eine mittags und eine abends.
I have two dates today, one at noon and one in the evening.
For planned meetings, the verbs 'haben' (to have), 'absagen' (to cancel), and 'verschieben' (to postpone) are often used. You can also 'eine Verabredung treffen' (make an arrangement), but that more often refers to the process of planning.
Ich kann heute leider nicht, ich muss unsere Verabredung absagen.
Unfortunately I can't today; I have to cancel our date.
A 'Verabredung' (date/meetup) typically takes place in a private or social context, for example with friends, family, or a partner. There are other words for business or formal meetings.
Sie hat eine romantische Verabredung mit ihrem Freund.
She has a romantic date with her boyfriend.
appointment / deadline
'der Termin' and 'die Verabredung' can both mean a planned meeting. 'Termin' is neutral and often fits official or organized situations, for example at the doctor, in an office, or at a government office. 'Verabredung' sounds more personal and is more suitable for private meetups with friends or acquaintances. In addition, 'Verabredung' can also mean the act of arranging a meeting. The words can be confused because both can have a time and a place. As a guide: at the doctor, you usually have a 'Termin'; with friends, it is more likely a 'Verabredung'.

Wir haben am Abend eine Verabredung mit Freunden im Park.
We have plans to meet friends in the park this evening.
Am Dienstag ist Herr Langes Termin beim Arzt.
Mr. Lange's doctor's appointment is on Tuesday.