On Thursday, many people were remembering the American writer Theodore Seuss Geisel – better known as "Dr. Seuss."
Geisel is one of the world's most famous authors of books for children.
March 2 would have been his 113th birthday. He was born in 1904 in Springfield, Massachusetts. He died in 1991.
In his honor, March 2 is known as both "Dr. Seuss Day" and, in many places, "World Book Day." The aim of the observance is to celebrate literature and urge children around the world to read.
On Thursday, the hashtags #DrSeuss and #WorldBookDay were two of the top trending topics on Twitter.
Dr. Seuss is known for his fantastical and humorous books for young children. His books are filled with colorful pictures and fun rhymes. Dr. Seuss' works include "The Cat in the Hat, "Green Eggs and Ham" and "The Lorax."
Dr. Seuss helped generations of children learn to read - and to love reading. His books have been published in some 20 languages.
Many people used "World Book Day" to express thanks for Dr. Seuss' books. One person tweeted "Thank you for making life more colorful."
Others honored other favorite authors, including Roald Dahl, Maurice Sendak and JK Rowling.
For bookworms, however, every day may seem like #WorldBookDay. A "bookworm" is an informal name for someone who loves to read.
As one person tweeted, "in my world, every day is World Book Day."
If you missed out on World Book Day, you will have another chance later this year to celebrate books and reading. The United Nations marks World Book and Copyright Day on April 23. That is the date that several of the world's greatest writers died. They include England's William Shakespeare and Miguel de Cervantes of Spain.