A Walkthrough (or Walkthru, or FAQ) is basically an extensive guide to get you through a game. There are a few here on Wikia Gaming, but most people go to GameFAQs. GameFAQs' walkthroughs are basically imageless, less glossy versions of strategy guides that are available in stores, whereas sites such as IGN and GameSpot, unconstrained by text-only rules, are able to include many illustrations to accompany and explain their walkthrough text.
The advantage strategy guides have over most online walkthroughs is that they are usually officially licensed and thus are heavily illustrated, resulting in guides rich in maps and character art, sometimes even exclusive to these works. Online walkthroughs have typically fewer images (or, in the case of GameFAQs' and IGN's user-submitted guides, no images at all) and usually no maps, but this is made up for by the fact that they are usually free.
Increasingly, fansites are producing highly illustrated works constantly updated with the latest user-discovered bugs and secrets. Guides written in a wiki environment are also free of such constraints. The comprehensiveness of and free access to such guides may one day challenge commercial guides.
Regardless, when well written both mediums can get you through the game just as easily.
Walkthroughs are commonly confused with playthroughs. A Playthrough is a recorded video showing a videogame being played by a gamer usually as a form of entertainment. It should be noted that "a gamer" does not have to be a human such as a computer using lexicographic ordering and time travel: http://www.youtube.com/watch?v=xOCurBYI_gY#t=6m10s . Playthrough videos do not require the game to be fully completed. As such, they are usually less extensive and may not cover all the hidden secrets and details in any given game. Playthrough videos are often beneficial as demonstrations for gamers to determine whether or not they want to purchase or play the game and are often beneficial for developers to observe and learn from their mistakes by discovering bugs or other room for improvement. There are four types of playthroughs: Longplays, Let's Plays, Speedruns, and Game Replays.
A Longplay is the most extensive form of playthroughs and is "created with the intent of completing it as fully as possible, mainly for the purposes of nostalgia, preservation, and possibly as a walkthrough" http://en.wikipedia.org/wiki/Longplay . These are often the least common form of Playthroughs due to the time, effort, and commitment involved towards making them as well as the concern for the amount of memory storage required for it. They can be thought of as movies based solely on the game.
A Let's Play (LP) is arguably the most common form of playthroughs, and many are found on the popular video sharing platform YouTube . LP videos are often made for the entertainment of their viewers, and as such, are usually encompanied by commentary often humorous in nature. Fighting and racing games are common subjects for LP videos due to their replayability. Horror games is also a common subject for LPs due to viewers wanting to see the reactions and responses of their favorite hosts or fellow players. LPs may also encompass games with a meaningful storyline or plot. In such cases, they can be thought of as episodes or journal records for an individual playing a game.
A Speedrun, if not LPs (see above), may also be the most common form of playthroughs. They are often created as entertainment or competition to set a world record on who can complete an entire game or level of a game the fastest (i.e. the shortest amount of time). Some speedruns have a specified set of conditions to vamp up the difficulty or to prevent players from exploiting a glitch or bug in the game.
Game Replays are unique in that the game actually generates the playthrough video for its players to view. Game Replays (also known as "Instant Replays") are traditionally shown in sports, racing, and fighting games to highlight a specific event or action. Recently, game replays are also used in shooting and RTS games to help prevent cheating in multiplayer environments, or so players can learn from one another valuable skills or useful techniques in the game. Some users may upload their Game Replays for entertainment purposes to mimick that of LP videos.
- GameFAQs, offering free text-only hosting of user-submitted guides
- Open Game FAQs, an editable GameFAQs "alternative" currently producing mostly text-only guides
- IGN Guides produces moderately illustrated guides, the newest ones only available to IGN Insider subscribers
- GameSpot also produces online guides, but these are usually free to GameSpot Basic subscribers
- Wikibooks hosts many editable guides with varying degrees of illustration
- RPGClassics produce fully illustrated guides but only deal in RPGs
- Gameinfo aims to produce fully illustrated walkthroughs akin to commercial strategy guides