Jessica Jones was a character Brian Michael Bendis retconned into the MU back in 2001 in her own book called Alias. She worked as a private investigator, usually taking jobs from more established MU characters, but in a gritty, pulpy, noirish fashion that made all the typical fantastical comic book shit seem a little more grounded. As she was working these jobs in the present, the story would sometimes delve into her tragic past as a failed costumed hero.
Anyway, everybody loved Alias, and when it ended Marvel tried to keep Jessica relevant by shoehorning her into other shit by having her marry Luke Cage and have his kid, etc. A lot of people are now pissed about her recent treatment, as she's mostly used in stories as Luke's nagging wife, as opposed to being the strong protagonist she was originally.
And then they made a show about her!