After a very long clause and a very long wait, here is a nice short clause (and no wait at all, as long as you read it immediately rather than rush off to make a cup of coffee).
15. Other Rights
The Author hereby grants to the Publishers exclusive licences for subsidiary rights, excluding film, television and merchandising rights.
exclusive licence = only the publisher is allowed to do any of the following things (so you can't market your own line of knitted characters or jelly bean flavours named after things in your book)
subsidiary rights = rights to produce the work in other formats or produce spin-offs from the work
merchandising rights = the right to sell products badged with your characters or other aspects of your work, even creating a whole brand identity. This can be clothing, food, lunchboxes, stickers, perfume, sticking plasters, condoms.... anything
The clause as worded here is a very bad deal. Don't agree to a rights grab like this. Unless electronic rights are mentioned elsewhere in the contract (in this case, they were in clause 1), have them excluded here. Other subsidiary rights you might like to retain include animation, computer game, and theme park rights. There is a potential for overlap between film, animation, machina and electronic rights, but this clause is just about keeping them all so we don't need to worry about that issue just now.
The real problem with a clause worded like this is that you are granting the publisher all undiscovered rights. There may be highly profitable rights just around the corner using a technology we don't yet imagine. No-one would have predicted iPad application rights ten years ago, for instance. Specify the rights the publisher can have, rather than those you want to keep - all other rights you should retain. Here's my punt for the next 50 years: DNA/genetic engineering rights - using genetic engineering to manufacture real living pets that are versions of the animals or monsters in your book, or to produce living dolls of the characters. These may be soft-tissue living entities with no consciousness (a sort of zombi-ised version) or something more autonomous.
Do as I say, not as I do: this contract was negotiated by my agent, not by me. At the time, I was severely depressed and coping with a very seriously unwell daughter - I wasn't paying attention and just signed. It's also for a very short book (it should come out as a graphic novel later this year). I would not accept this clause normally and would have done a good deal of stropping.