At one point large estates were 'entailed'. See
http://en.wikipedia.org/wiki/Fee_tail for more, but basically when you inherited an estate you didn't gain full property rights to it. You couldn't sell, subdivide, or otherwise part with the estate and you had to leave it to your Heir (usually the closest male blood relative) instead of leaving it to whoever you wanted. So you could have a case where none of your daughters could inherit because legally the estate had to go your third cousin - which is the plot of the first season of Downton Abby.
As you can see on the wiki link provided above, those entails have been more or less abolished by law. The closest thing you have to it now is a 'life interest' - where effectively everything is held in trust and you have the use of it while you live, then it goes to the next beneficiary of the trust.
Back 40 or 50 years ago, it was possible to challenge a will when a child wasn't mentioned in it. You could claim that your parent (and his lawyers) overlooked you when writing the will and fight it out in court - at least as long as you were a legitimate child (bastards got the short end of the stick). Different areas had different ways around that. Example, if your son was named Bill:
"And for my son Bill, I have made sufficient arrangements for him in life and have no need to make any now." - was used in some places.
"And while I acknowledge my son Bill I am purposely excluding him from the estate." - was used in others.
"And to my son Bill, I leave the sum of one (1) dollar while excluding him from the remainder of the estate." - was the way you did it in other places.
But I believe that's all changed as the laws adopt to non-traditional families. Now you can exclude all of your children as you leave your estate to your dog, to that waitress you liked at your local pub, to the charity of your choice, or your third wife's stepkids if you want. The only current exception (and it's not in place everywhere) is that your spouse is generally entitled to what the spouse would have gotten in a divorce (i.e. your spouse keeps the spouse's share of the marriageable property when you die).
Goodgulf