Computer Keyboard

The ~ is called a tilde (till-dee). It's used before numbers to mean "approximate"; it's also used as a diacritic mark in Spanish (over the N in "jalapeno", for example) and some other languages.

The ` is called a backtick. I have no idea what its intended purpose is, but back in the days of plain text, it was sometimes used as a poor substitute for an opening curly-quote. It's also used (on Macs, anyhow) as a dead-key for the grave accent.

Wikipedia has some good--though lengthy--information on both topics.

http://en.wikipedia.org/wiki/Backtick

http://en.wikipedia.org/wiki/Tilde

Well, in the language of math, ~ means, "is similar to."

These are normal characters (not much used though.)

. . . unless you are a computer programmer, or writing in Spanish (which uses the tilde), French (which uses the grave accent), Italian (which uses the grave accent), or any other language that uses these diacritics.

Not quite. All languages use the tilde (as the "approximate" sign, not as the spanish diacritic that goes over the letter like this "ñ": you can't achieve this latter with the "~" key). The "`" is a backtick (or backquote), and not the accent grave like in "è"-- again, "`" is a character, not a diacritic, which the accent grave is. You can't type a backtick "in" over another character. These things look similar -- just like 1 and I sometimes look similar, or zero and the O -- but they're not the same as far as the keyboard. Well, anyway, it doesn't matter.

Go into MS Word or some similar program, and press 'ctrl-shift-~' followed by 'n'. Then you get the 'ñ'. Using the same idea with the backtick or backquote, you can generate a grave accent: 'ù'. I believe that they were defined in ASCII with this dual purpose in mind (though I could be mistaken), mimicking the typewriter.

This tilde is a portuguese tilde. You can use in this words, for exemple:

Caminhão (truck)
Avião (airplane)
Mão (hand)
Mãe (mother)
Irmão (brother)
Irmã (sister)

tks

To create special characters on the keyboard, hold the ALT key down and type the following number on the numeric keypad; then, release the ALT key.

Ç = 128
ü = 129
é = 130
â = 131
ä = 132
à = 133
å = 134
ç = 135
ê = 136
ë = 137
è = 138
there's more...
ñ = 164
Ñ = 165

There are plenty of pages which show the entire list of characters -- ¿, ½, ¢, £, °, etc. -- so I won't bother here.

I don't think that the tilde actually means "roughly equal to" as Lia suggested. I've always known the "roughly equals" sign as a equals sign, but wiggly, like two tildes on top of each other. I think we just use the tilde because it's the closest to it on a normal keyboard. Just as we use * for "multiply" sometimes, but that's not really what it means.

In Unix scripting, PHP and other programming languages the ` is used to denote parsing a specific command string. For example

x=`cat file.txt` which will return the value of the file.txt to the variable reference $x.

In JavaScript the ` is equiv. to the eval() function.

Patrick, the tilde is used to mean approximately equal to. So is the wavy equal sign you mentioned (like two tildes one on top of the other). A third way is to write a normal, straight equal sign and put a tilde on top of it. All three mean the same thing. Also, a tilde can be used to indicate a range, like 1~5 meaning 1 to 5.

Bob, if you use ALT-xxx to make characters, you should always put a leading zero, e.g., ALT-0128, not ALT-128. In some cases it doesn't matter, but in others, it won't work without the zero. Also, to repeat what you already said, you must use the numeric keypad. The numbers above the letters will not work.

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By the way, Adam, it's pronounced "till-duh", not "till-dee".

When I met this symbol in maths it was pronounced "twiddles" and meant "is equivalent to".