Within each colored belt (white, blue, purple, brown), you can earn up to 4 stripes. Stripes mark progression within a belt level. They are awarded by your professor based on time, technique, and consistency.
The fourth stripe is typically the last marker before promotion to the next belt color. Some academies are strict about stripes; others give them freely. There is no IBJJF rule on exactly when stripes must be awarded.
Black belt uses a different system: degrees from 1st to 6th, each requiring 3+ years. After 6th degree, you progress to red and black, then red and white, then red — but those are reserved for grandmasters.