NDEF (NFC Data exchange format) is a method of transferring (relatively small amounts of) information from a passive or actively emulated tag by way of "records" which specify the type of information is being received and the function it is meant to have.
iPhones do not have a full suite of NDEF compatibility, the reason for this is unknown (to me at least), what this means is the background polling on iPhones will not interpret some specific record types, with compatible NDEF records, a notification will pop up directing the user to follow the received data into its respective app to complete whatever action was intended by the record.
Below are the options offered by NFC Tools on IOS for NDEF Encoding, some of the options below are other record types but with a specific function IE social links are just URLs.
