If you want to disable the ‘Cut / Copy / Paste’ invoked by holding down on an element in Safari on the iPhone or iPad you can use the CSS user-select
However, as stressed by Apple, this should only be disabled on a per element basis, and never applied to the whole document.
To disabled selection on elements in every browsers:
user-select: none; -moz-user-select: none; -webkit-user-select: none; -ms-user-select: none;
Simple and easy.