This is the 17192nd most frequent Russian word.
сторонних
"Сторонних" means "external" or "outsider."
The word 'сторонних' means 'external' or 'outside' and describes interference from outside sources.
Он избегает сторонних вмешательств.
He avoids external interference.
Here 'сторонних' refers to observers who are external or unrelated to the group organizing the event.
Сторонних наблюдателей на мероприятие не допускают.
External observers are not allowed at the event.
In this context, 'сторонних' describes developers that are third-party, not internal to the company itself.