Good Debt:
A horrible term that's subject to abuse.
Here's my definition of Good Debt:
"Good Debt is debt that you are paid to have at a guaranteed profit."
Example: Get student loans at 3% and buy US Treasuries with those loans that pay 5%.
Obviously, this is hard to do. But it is "Good Debt".
Acceptable Debt
Acceptable Debt has a reasonable chance of improving your circumstances beyond that which it reduces your circumstances by its very existence. Therefore, it must be appropriate in size to the gains it can reasonably be expected to produce and not have a downside that is likely to have terrible repercussions. I.e., a game of Russian Roulette with $1,000,000 per spin has a 5/6ths chance of getting rich and a 1/6th chance of dying. Great upside but unacceptable downside!
Example: Student loans of $30,000 that will likely lead to a position paying $50,000.
Not an Example: Student loans of $180,000 that will likely lead to a position paying $30,000, or which only have a 1% chance of getting into a decently paying position.
Example: A fixed rate, 30 year mortgage at 2.75% on a dwelling that is at an affordable price, where inflation is expected to average 3% a year.
Not an Example:
Bad Debt
All debt is assumed to be bad debt unless proven otherwise.