Some of those terms are fairly common, and its probably expected that the user would either know them, or at least be able to get some idea as to the usage from the context.
Index for example is a numerical value that goes in order from zero up, and is often used to distinguish multiple items from each other.
Tag on the other hand is a generic term often used in html as a label that a user can give to an object giving them the ability to reference that object by name later on. Here it is used by the Audio object to name a sound.
Im not sure what bin means here, but you can be fairly sure its a number, and can be used with some experimentation.