FIP: Stands for Fielding Independent Pitching. FIP = ((13*HR)+(3*(BB+HBP-IBB))-(2*K))/IP + constant. The ‘constant’ is a number that gets the FIP onto the same scale as ERA. Razzball’s stat feed does not separate BB from IBB so those are not deducted. This, as well as slight differences in calculated the constant, will lead to slight differences in FIP vs. other data sources. For more info/background on FIP, see here.
FIP-ERA: In general, FIP and ERA should be close to equal with much of the difference tied to luck (HR rates, BABIP, etc.) So pitchers with a negative number are more likely to see their ERA increase while pitchers with a positive number are more likely to see their ERA decrease.