Oracle: what is the “instantclient” connection string format?

Question

and how does it differ from the regular connection string?

Answer 1

The format is:

name/pass@//host:1521/instance

Standard Oracle connect strings typically look like

name/pass@tnsentry

Where tnsentry has been defined by one of several means such as a tnsnames.ora file. idstram's answer has an excellent pointer if you're looking for more details.