This page is broken down by the Genre and it’s definition.   Just like in Anime, it tells/shows the Genre, so it does  with Manga!  😛

Text pulled from Mangaupdates.com

Action

A work typically depicting fighting, violence, chaos, and fast paced motion.

Adult

Contains content that is suitable only for adults. Titles in this category may include prolonged scenes of intense violence and/or graphic sexual content and nudity.

Adventure

If a character in the story goes on a trip or along that line, your best bet is that it is an adventure manga. Otherwise, it’s up to your personal prejudice on this case.

Bara

Men’s Love, or ML.

Comedy

A dramatic work that is light and often humorous or satirical in tone and that usually contains a happy resolution of the thematic conflict.

Doujinshi

Fan based art inspired by official anime or manga.

Drama

A work meant to bring on an emotional response, such as instilling sadness or tension.

Ecchi

Possibly the line between hentai and non-hentai, ecchi usually refers to fanservice put in to attract a certain group of fans.

Fantasy

Anything that involves, but not limited to, magic, dream world, and fairy tales.

Gender Bender

Girls dressing up as guys, guys dressing up as girls.. Guys turning into girls, girls turning into guys.. I think you get the picture.

Harem

A series involving one male character and many female characters (usually attracted to the male character). A Reverse Harem is when the genders are reversed.

Hentai

Adult sexual content in an illustrated form where the FOCUS of the manga is placed on sexually graphic acts.

Historical

Having to do with old or ancient times.

Horror

A painful emotion of fear, dread, and abhorrence; a shuddering with terror and detestation; the feeling inspired by something frightful and shocking.

Josei

Literally “Woman”. Targets women 18-30. Female equivalent to seinen. Unlike shoujo the romance is more realistic and less idealized. The storytelling is more explicit and mature.

Lolicon

Representing a sexual attraction to young or under-age girls.

Martial Arts

As the name suggests, anything martial arts related. Any of several arts of combat or self-defense, such as aikido, karate, judo, or tae kwon do, kendo, fencing, and so on and so forth.

Mature

Contains subject matter which may be too extreme for people under the age of 17. Titles in this category may contain intense violence, blood and gore, sexual content and/or strong language.

Mecha

A work involving and usually concentrating on all types of large robotic machines.

Mystery

Usually an unexplained event occurs, and the main protagonist attempts to find out what caused it.

Psychological

Usually deals with the philosophy of a state of mind, in most cases detailing abnormal psychology.

Romance

Any love related story. We will define love as between man and woman in this case. Other than that, it is up to your own imagination of what love is.

School Life

Having a major setting of the story deal with some type of school.

Sci-fi

Short for science fiction, these works involve twists on technology and other science related phenomena which are contrary or stretches of the modern day scientific world.

Seinen
From Google:

Seinen means “young Man.” Manga and anime that specifically targets young adult males around the ages of 18 to 25 are seinen titles. The stories in seinen works appeal to university students and those in the working world. Typically the story lines deal with the issues of adulthood.

Shotacon

Representing a sexual attraction to young or under-age boys.

Shoujo

A work intended and primarily written for females. Usually involves a lot of romance and strong character development.

Shoujo Ai

Often synonymous with yuri, this can be thought of as somewhat less extreme. “Girl’s Love”, so to speak.

Shounen

A work intended and primarily written for males. These works usually involve fighting and/or violence.

Shounen Ai

Often synonymous with yaoi, this can be thought of as somewhat less extreme. “Boy’s Love”, so to speak.

Slice of Life

As the name suggests, this genre represents day-to-day tribulations of one/many character(s). These challenges/events could technically happen in real life and are often -if not all the time- set in the present timeline in a world that mirrors our own.

Smut

Deals with series that are considered profane or offensive, particularly with regards to sexual content

Sports

As the name suggests, anything sports related. Baseball, basketball, hockey, soccer, golf, and racing just to name a few.

Supernatural

Usually entails amazing and unexplained powers or events which defy the laws of physics.

Tragedy

Contains events resulting in great loss and misfortune.

Yaoi

This work usually involves intimate relationships between men.

Yuri

This work usually involves intimate relationships between women.