Electrical – RSS Error

In this case it probably means Root of Sum of Squares.

The chart on the linked page is actually a dynamic chart generated using Javascript, so we can look at the code. The last line combines a couple of error sources as:

var total_error_room_temperature = Math.sqrt(Math.pow(total_vos_error_temperature,2)+
    Math.pow(gain_error_temperature,2));

So the function used in the chart to combine errors is:

$$e_{total} = \sqrt{e_1^2 + e_2^2}$$

This is a the square root of the sum of the squares.

The other meaning for RSS that appears to be more common in general is Residual Sum of Squares, used in linear regression calculations, but does not apply here.