When you use a stock broker to buy shares, you can often find the share you want by its name. However, some companies have similar sounding names, and some companies issue more than one share. You can use the ISIN code to make sure you’ve got the right share.
See also TIDM
An issuer is defined in the AIFM Directive as a “legal entity governed by private or public law” whose securities are admitted to trading on a regulated market and which has its registered office in the European Union.