1117 Regulator input voltage
The 1.3 V is the "dropout" voltage for the linear regulator. What it means is that for any Vin &lt; Vout + 1.3 V, the output is not guaranteed to be the specc'ed Vout; 5 V in your case. Vout will likely be approximately Vin - 1.3; depending on output current.

From the TI datasheet (LM1117 Datasheet) :


So from a design perspective, you would want the input voltage to be at LEAST 6.3 V, and anywhere up to 15 V (per the datasheet recommended operating conditions) to "guarantee" a clean 5 V out.

Edit 2017-12-26: changed above bold section from 20 to 15 V per recommended operating conditions, instead of absolute maximum's. Thank you @SamGibson for the wise recommendation