farewell party; goodbye party; send-off party
A social gathering held to say goodbye to someone who is leaving, such as a colleague transferring or a friend moving away.
See also: 告別式
Next week we'll hold a farewell party for Mr. Tanaka, which will also serve as his send-off.
memorial gathering; gathering to remember a deceased person
A gathering to honor and remember someone who has passed away. Similar to 偲ぶ会, but お別れ会 can be used for less formal, more personal memorial events.
See also: 偲ぶ会
We had a goodbye party in class for a friend who was transferring schools.
Only close friends and family gathered for my grandmother's memorial gathering.
送別会 is a send-off party for someone leaving a workplace or group, while お別れ会 can be used more broadly for any farewell, including personal goodbyes.
Compound of お (honorific prefix) + 別れ (farewell, parting) + 会 (gathering, meeting).