Literally meaning: to cease developing; become inactive or dull. When things are difficult, financially or otherwise, we scramble. Most of us throw as much against the wall as possible hoping something will stick. And when things are going extremely well, we're motivated to keep it that way. It's when things are just average, normal, that we can become stagnant.
There was a long stretch when our above-ground pool was unused. No filter running, no chemicals; stagnant. It became fairly grotesque, and the only answer was pumping every drop of water out, cleaning, and starting fresh.
Don't let months and years go by just doing the status quo. It doesn't have to be income related or for prospective work, but try something new. A hobby, a class, start something fresh.