NEW YORK (AP) — Happy Birthday, Twitter.

The social media site famous for hashtags and a 140-character "tweet" limit turned 10 years old Monday, having evolved from what was originally billed as a "microblogging" site into one of the Internet's most influential means of communication.

But after a long streak of robust growth that turned it into one of the Internet's hottest companies — despite not turning a profit — Twitter's expansion has slowed dramatically during the past year-and-half. At the end of 2015, it had about 320 million active users, far short of social networking leader Facebook and its 1.5 billion users.

Twitter Inc. executives have acknowledged their struggle to convince people the company provides an essential service and recently tweaked Twitter's format to make it more user-friendly.

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