This is based on the loan-to-equity ratio, which is total liabilities divided by equity (assets minus liabilities). Leverage is about how much debt is boosting equity so that a company can get the assets it needs. A low leverage company is using proportionately less debt than its industry peers.
For example,
Tesla $37.25B assets, $28.08B liabilities, $9.17B equity, 3.06 D/E.
GM $246.6B assets, $206.5B liabilities, $40.1B equity, 5.15 D/E.
Ford $258.5B assets, $225.4B liabilities, $33.2B equity, 6.79 D/E.
Tesla has substantially less leverage than Ford or GM. Corporations often like to use greater leverage to improve the return on equity. That is, the cost of capital from debt is typically less than for equity, so higher leverage allows a smaller equity investment to yield higher returns. Companies with thin margins and little growth, like Ford and GM, are only able to deliver an attractive return on equity through leveraging. The downside, of course, is that more debt means more risk for shareholders.
Tesla, OTOH, has been using positive free cash flow to delever, reduce the D/E ratio. So far, the market seems to appreciate the reduction in liquidity risk that this implies, while the opportunity to grow equity remains very high for Tesla. So Tesla does not need to use lots of debt either to grow fast or to spice up ROE. Indeed, the equity only $2.3B capital raise a few months ago seems to be a substantial part to supporting the current high valuation around $1000/sh. That one raise improved D/E from 4.09 to 3.06. Shareholders are more confident that Tesla has both plenty of liquidity and capital for expansion. Had Tesla issued $2.3B in debt instead, the D/E ratio would have been 4.42 instead of 3.06. Either way, liquidity and capital available for expansion would have improved, but Tesla would have substantially more leverage had it borrowed. Likely, investors would have worried more about the ability to pay back $2.3B in incremental debt than an concern about dilution.
I think part of this issue here is that that Tesla has been so traumatized by shorts attacking the stock as a potential bankruptcy case that it is simply a relief to have low leverage. Lower leverage destroys the TSLAQ case. Total debt (excluding non-recourse product financing) is just $8.3B while cash is $8.1B. For a company with market cap over $180B, this is really quite a trivial debt load. That is, Tesla is in a very strong position to be able to raise more capital from equity and delever even more. It doesn't need to, and further deleveraging might not be as well received by shareholders. But for now, I think the last equity offer was a really savvy move.
Edit. Note that there are different variants of D/E ratios floating around. Some focus only on the long-term portion of debt while others include all liabilities in the numerator. I am following the latter, most inclusive definition, per
Debt-To-Equity Ratio – D/E.