The pgm_read_byte_near() is a macro that reads a byte of data stored in a specified address(PROGMEM area).
The pgm_read_byte_near() is defined in hardware/tools/avr/avr/include/avr/pgmspace.h as below.
#define pgm_read_byte_near(address_short) __LPM((uint16_t)(address_short))
The input is address_short and the macro converts the address_short to uint16_t, then calls __LPM() macro.