What does rand() % 2 mean?

I've come across this program but I can't seem to figure out this part. Please help me understand what is the use of rand() % 2 and how is it a condition to determine whether it's credit or debit?

#include<stdio.h>
#define NUM_TRANS 400
void * transactions(void * args) {
  int v;
    
  for(int i = 0; i < NUM_TRANS; i++) {
    v = (int) rand() % NUM_TRANS;
  
    if (rand() % 2) {
      // Crediting to user
      
     
      pthread_mutex_lock(&balance_lock);
      balance = balance + v;
      pthread_mutex_unlock(&balance_lock);
      
      pthread_mutex_lock(&credits_lock);
      credits = credits + v;
      pthread_mutex_unlock(&credits_lock);
      
    } else {
      // Debiting from user

      pthread_mutex_lock(&balance_lock);
      balance = balance - v;
      pthread_mutex_unlock(&balance_lock);
      
      pthread_mutex_lock(&debits_lock);
      debits = debits + v;
      pthread_mutex_unlock(&debits_lock);
    }
  }
}