A sabotage as an
industrial action:
First of all, a sabotage is not necessarily only destruction of machinery as it is often understood. We have to put a sabotage in a bigger picture i.e. examine a sabotage in the light of class conflict or of struggle against work. Some definition I have come across said: "A form of direct action by workers against employers through obstruction of work and/or lowering of plant efficiency."
In this sense also go-slow, work with poor quality, absenteeism etc. can be counted to be some sort of sabotage. They all reduce the output of capitalist production and aim to workers' emancipation. Also when you use means of production for your personal entertainment or if you print out anarchist leaflets in your office, you can claim to be a proud sabotager. One important notion should be added: It is not a sabotage if you play solitaire in your work time unless you intend to reduce the output.
A sabotage can be defensive or aggressive. Whereas the former aims to preserve the results of workers' struggles, the latter aims to improve working conditions, salary or it may even be used as the mean to achieve workers' power.
Whilst syndicalists are great favors of sabotage, communists often see it as counterrevolutionary action because communism can be achieved only by huge development in production.