parallel
parallel / simultaneous
Happening at the same time or side by side.
Die beiden Konferenzen finden parallel in unterschiedlichen Räumen statt.
The two conferences are taking place in parallel in different rooms.

Loading your saved state.
parallel / simultaneous
Happening at the same time or side by side.
Die beiden Konferenzen finden parallel in unterschiedlichen Räumen statt.
The two conferences are taking place in parallel in different rooms.

'Parallel' is very often used in the construction 'parallel zu etwas' (parallel to something). The preposition 'zu' requires the dative here.
Parallel zur Straße verläuft ein schöner Radweg.
A beautiful bike path runs parallel to the road.
'Parallel' can stand before a noun as an adjective or as an adverb describing a verb. The form of the word does not change.
Das sind zwei parallele Prozesse.
Those are two parallel processes.
The context usually makes the meaning clear. Words like 'Linien' (lines) or 'Abstand' (distance) point to geometry, while 'Prozesse' (processes) or 'Berechnung' (calculation) point to computer science.
Zeichnen Sie eine Gerade parallel zur y-Achse.
Draw a straight line parallel to the y-axis.
In the meaning 'gleichzeitig' (simultaneously), 'parallel' is often combined with verbs such as 'stattfinden' (to take place), 'laufen' (to run), 'arbeiten' (to work), or 'existieren' (to exist).
Man kann nicht zwei Vollzeitjobs parallel machen.
You can't do two full-time jobs in parallel.
simultaneously / at the same time
'gleichzeitig' and 'parallel' can both describe that two things happen at the same time. 'gleichzeitig' mainly emphasizes the time: two actions happen in the same moment. 'parallel' emphasizes more that two processes run side by side, often over a certain period of time. This fits, for example, with projects, courses, or work. The words can be confused because both have to do with the same time. A simple guide is: for a moment or an exact point in time, 'gleichzeitig' fits better; for two ongoing processes, 'parallel' often fits better.

Im Büro laufen zwei Projekte parallel, deshalb ist das Team sehr beschäftigt.
Two projects are running in parallel at the office, so the team is very busy.
Zwei Kinder haben gleichzeitig die gleiche Antwort gerufen.
Two children shouted the same answer at the same time.