This is a vintage P25 or No. 5 photography flash bulb, likely manufactured by Sylvania or General Electric (GE).
These are single-use chemical flash bulbs that were popular for use with cameras from the late 1950s through the 1960s.
They contain a small amount of aluminum foil in an oxygen atmosphere, which ignites to create a bright flash of light.
The bulbs are designed to be used with specific vintage cameras and flash holders.
They are known for their high light output, with the No. 5 bulb having a peak brightness of approximately 1,450,000 lumens.