Chili and pepper are not the same thing however people just refer to chilies as peppers interchangeably.  As far as I'm aware the difference is that peppers contain pipirine coming from the piper plant(such as black pepper, long pepper) whereas chillies contain capsaicin coming from capsicum plant and this is mutually exclusive.    This scoville chart https://www.pinterest.com/pin/148196643973566417/ shows bell peppers as containing no capsaicin so why is it in the list and is it considered a chili?  I'm confused Please clarify. 
When people talk about "peppers" (plural), they are referring to the fruit of capsicum plants.  This includes both hot and "bell" peppers.  The singular "pepper" is used to talk about "peppercorns", which are in no way related to capsicums.  And although white, green and black pepper are different ways of processing the same spice (containing pipirine), the term "peppercorn" is also used to talk about botanically unrelated spices (red, pink, scichuan, etc.)  Here's the current text of the relevent section from Translating cooking terms between US / UK / AU / CA / NZ :         Capsicum (AU) / bell pepper (US) is a pepper (UK). Note that for people with a biology background 'capsicum' also includes hot peppers (aka chilies or chili peppers)   Peppers (US) (note the plural), is typically short for chili peppers unless qualified as sweet peppers or bell peppers, or specified as peppercorn.   Colored peppers (US), (eg, red peppers, green peppers), typically refers to bell peppers unless qualified (eg, 'hot red peppers', 'small red peppers')   Pepper (US) (note the singular) refers to black peppercorns unless otherwise qualified.   Red pepper (US, note the singular) refers to dried, red chilies (typically cayenne) that has been dried and ground or crushed.     