What does the ISO or ASA of a film indicate?

ASA acronym for American Standards Association - hence ASA400 on films is the standard film speed of 400. ISO is International Standards Organization. the two values are identical, for once there is no separate ( Metric) or different European film standard. The Germans do use the DIN ( German Industrial Norms) standards this is such that that- DIN 27 is equivalent to ASA 400. ASA and DIN are the only common film standards used today. There you have it. Get yourself a Photometer and the meanings of the various scales will be self-evident. Besides you can learn much about differing exposure values- for nearly every potential shot there are more than one possible (answers) so there are considerable variables around. Experiment!