A bridge loan provides cash to extend runway between rounds. It's most often structured as a SAFE or convertible note from existing investors and converts into the next priced round. Bridge loans are common when a company needs more time to hit milestones before the next financing.
The term is sometimes used interchangeably with 'bridge round'. The distinction is mostly contextual: 'bridge loan' emphasizes the short-term debt-like aspect; 'bridge round' emphasizes that it's a real financing.