In 1571, the Spaniards found the people in Manila and other places writing on bamboo and specially prepared palm leaves using knives and styli. They were using the ancient Tagalog script which had 17 basic symbols, three of which were the vowels a, i, and u. Each basic consonantal symbol had the inherent a sound: ka, ga, nga, ta, da, na, pa, ba, ma, ya, la, wa, sa, and ha.
A diacritical mark called kudlit modified the sound of the symbol. The kudlit could be a dot, a short line, or even an arrowhead. When placed above the symbol, it changed the inherent sound of the symbol from a to i; placed below, the sound became u. Thus a ba with a kudlit placed above became a bi; if the kudlit was placed below, the symbol became a bu.
It was a simple and elegant system that was called baybayin. In 1914, the newer term alibata was introduced by Dean Paul Versoza of the University of Manila. He claims the term comes from alif, ba, and ta, the first three letters of the Maguindanao arrangement of the Arabic letters. He did not explain why he chose a totally unrelated writing system to name the script.
The Tagalog script was a syllabary, which means that each symbol represents a complete syllable. This is in contrast to our Latin alphabet where each symbol represents a phoneme, the smallest unit of the sound of speech. It is this distinction that makes it difficult for many people steeped in alphabetic systems to understand the correct way of using the Tagalog script. (By Hector Santos)
(I found these pretty cool, imagine if we're still using these today?)