@AlexC has already provided the correct answer, but I thought I'd provide a bit more details.
The breakeven inflation (still the mostly widely used practitioner terminology) is defined as follows:
$$ \text{breakeven inflation} = \text{nominal yield} - \text{TIPS yield}. $$
It is called the breakeven inflation ("BEI") because if ex-post realized inflation is identical to the ex-ante BEI, then an investor should be indifferent between investing in TIPS and buying the nominal comparator (both would generate the same returns).
As @AlexC mentioned, TIPS breakeven is closely linked to inflation expectation, but in reality, it is a highly noisy measure of the former. TIPS are much less liquid compared to nominal Treasuries, so investors typically require a HIGHER yield to compensate for the illiquidity risk. Of course, this makes breakeven inflation LOWER than the true inflation expectation. This was a huge problem during the early years of the TIPS program (investors were not familiar with TIPS) and during the 2008 financial crisis. The chart below plots 10-year breakeven inflation against a market-based measure of 10-year inflation expectation:

As you can see, during the depth of the financial crisis, 10-year TIPS breakeven traded down to 0, but surely no one expected inflation to average 0% over the next 10-years! At the time, TIPS became so illiquid that their yields are substantially inflated.