parallel operation vs simultaneous operation

parallel operation and simultaneous operation both are nouns.

Word	Noun	Adjective	Verb	Adverb
parallel operation	Yes	No	No	No
simultaneous operation	Yes	No	No	No

As nouns, parallel operation and simultaneous operation are synonyms defined as:

parallel operation and simultaneous operation: the simultaneous execution of two or more operations

parallel operation (noun)	simultaneous operation (noun)
the simultaneous execution of two or more operations	the simultaneous execution of two or more operations