Was ist #elif?

Ich möchte den 90S8535 verwenden. Was bedeutet in diesem Zusammenhang
"elif" (else-if??)

#if defined(_AVR_AT90S2313_)
#  define OC1 PB3
#  define OCR OCR1
#  define DDROC DDRB
#elif defined(_AVR_AT90S4414_) || defined(_AVR_AT90S8515_) || \
      defined(_AVR_AT90S4434_) || defined(_AVR_AT90S8535_) || \
      defined(_AVR_ATmega163_)
#  define OC1 PD5
#  define DDROC DDRD
#  define OCR OCR1A#else
#  error "Don't know what kind of MCU you are compiling for"
#endif

#if defined(COM11)
#  define XCOM11 COM11
#elif defined(COM1A1)
#  define XCOM11 COM1A1
#else
#  error "need either COM1A1 or COM11"
#endif

mfg maxl