Similarities between flash memory and a camera flash?
Like a flood flash that illuminates an area, the flash memory is erased in a block. From the paper A NEW FLASH E2PROM CELL USING TRIPLE POLYSILICON TECHNOLOGY by MASUOKA et. al (1984) - emphasis by author(s): 



In very early memories, the block size was the entire chip and the erase time was quite long (something like a second). Still much, much faster than UVEPROM erasure times, and compatible with inexpensive packaging (no quartz window required).