What is meant by a high-level of debt in a company?

I've been trying to figure out if the companies I'm looking at have a high level of debt, but the more I looked into it, the less obvious it became.

Is there a magic ratio of equity/debt to be cautious of?

…or is it the level of debt in relation to the sector the company is in? Eg. how prisons and private security companies seem to have a high level of debt in relation to their income, but this is somewhat “normal” in this industry.