In management theory, a hygiene factor is something that is necessary but not sufficient for motivated, productive workers.
For instance, if the power were to go off in our office, we wouldn't be able to use the computers and productivity would plummet. In spite of this, you can't call electricity a major motivation.
Getting a hygiene factor wrong is a good way to demotivate; getting a hygiene factor right does not guarantee motivation.
Many human issues are hygiene factors. Fair treatment is a hygiene factor. So is pay. A salary increase produces at best a temporary motivation. If you expect "Equal pay for equal work", then finding out that you earn less than a colleague can be highly demotivating. Reversing demotivation due to human factors is not easy - if you lose trust, you have to win it back.
This all goes back to a guy called Frederick Herzberg, who distinguished hygiene factors from motivators in a book called The Motivation to Work in 1959. In his research he found, to his suprise, that the factors that demotivate were not simply the logical opposite of the factors that motivate. He distinguished "motivated" (influenced positively) from "demotivated" (influenced negatively) from "unmotivated" (not influenced - neither inspired nor embittered).
I don't know why the jargon term "hygiene factor" was chosen, but it seems to me to be an analogy with personal hygiene: We don't brush our teeth or wash our hands in order to gain success and fortune - we do it purely to avoid misfortune.
The brief list of hygiene factors given is Company policy, Supervision, Relationship with Boss, Work conditions, Salary, Relationship with Peers. The brief list of motivators given is Achievement, Recognition, Work itself, Responsibility, Advancement, Growth.
In short, there are a number of factors that can demotivate people if any of them is bungled. Demotivation is not the simple converse of motivation. While demotivation comes from outside, motivation comes from within.
Motivation can however be nurtured. While so many companies say things like At foobar systems we recognize the potential for achievement in our greatest asset: the extraordinary people who work here etc. etc. but walking the walk is harder.