to visit someone casually without prior arrangement
jemanden ohne vorherige Vereinbarung informell besuchen (jemanden ohne vorherige Vereinbarung informell besuchen)
"My neighbors often drop in for coffee in the evening."
"Meine Nachbarn kommen oft drop in für einen Kaffee am Abend." (Meine Nachbarn kommen oft **drop in** für einen Kaffee am Abend.)
to allow yourself to take a break and relax
to start suddenly (for war, fire, disease, etc.)
to look carefully for something, especially a good deal
to focus closely on a specific target or goal
to include a file or document with an email
to perform a task together with another party