Fortitude: Armor Rune Word - Diablo 2
Fortitude is one of the few Rune Words that works in both Weapons and Armor. This Rune Word is geared more towards melee fighters due to the +300% Enhanced Damage that it provides when put on armor. I see the question asked a lot online how the Fortitude Rune Word Enhanced Damage works on armor so let me try to answer...
Enhanced Damage is applied differently to your character when it is not on a weapon and is called "Off-weapon ED" or "Off-weapon damage" in these instances. Basically what the game does is it calculates your weapon damage first and all of the bonuses on your weapon; then it factors in your "off-weapon ED" and applies that to the total weapon damage done. There are good writeups about it here and this one is ok.
The short answer is yes, Enhanced Damage on Fortitude when put into your armor 100% boosts your Melee damage. To quote one of the websites I link to in the previous paragraph, "The combination of weapon Enhanced Damage and % Damage normally has the most significant impact on attack damage: for example, 300% Enhanced Damage results in 4 times base weapon damage while +300% Damage results in 4 times attack damage; together, this results in attack damage 16 times base weapon damage without any other damage bonuses."
Keep in mind that all Rune Words you create will retain any pre-existing bonuses found on the item. If you find a 'Superior' piece of armor with +Enhanced Defense, a Superior Weapon with +Enhanced Damage or a Helm/Weapon that has +Skill bonuses for a certain class, all of these will remain on the final Rune Word that is created. It's also possible to 'ebug' a piece of Ethereal Armor that you find which will increase the Defense bonuses by 50%, check out my Ebugging Guide for more information.
Farming High Runes: Out of all locations in the game one stands above the rest for farming specifically High Runes, the Countess during Act 1. The Countess has a guaranteed chance to always drop a High Rune and can even drop more than one. Check out my The Countess Farming Guide for more information.
Required Runes: 
El -- 
Sol -- 
Dol -- 
Lo
Level Req: 59
Other Req: Ladder Only
Slots: Weapons & Chest Armor
Both
20% Chance To Cast Level 15 Chilling Armor when Struck
+25% Faster Cast Rate
+300% Enhanced Damage
+200% Enhanced Defense
+((8-12)*0.125*Clvl) To Life (Based on Character Level) (varies)
All Resistances +25-30 (varies)
12% Damage Taken Goes To Mana
+1 To Light Radius
Weapons
+9 To Minimum Damage
+50 To Attack Rating
20% Deadly Strike
Hit Causes Monster To Flee 25%
Armor
+15 Defense
Replenish Life +7
+5% To Maximum Lightning Resist
Damage Reduced By 7
Fortitude Rune Word in Ebugged Wire Fleece.
Fortitude Rune Word in Ebugged Balrog Skin.
Continue to Weapon Fortitude Rune Word Page