A Primer to Fate/Stay Night [Unlimited Blade Works] Part III: REVELATIONS

Welcome to the third instalment of my Primer to Fate/Stay Night [Unlimited Blade Works] series, where I attempt to explain the Fate-verse (or Nasu-verse, after the creator of Fate/Stay Night, Kinoko Nasu) to first-time viewers of the aforementioned anime. This time, we shall dwell on some of the actual story elements of the anime.

If you wish to read the first two parts - and if you haven't, I suggest you do - then you may access them below:

Part I: INTRODUCTION
Part II: THE HOLY GRAIL WAR

NOTE: The following is based on the events of Fate/Stay Night [Unlimited Blade Works] only, up to episode 18 which is the latest episode at time of writing. As the series continues, I will be updating this post. Also, do note that this post will continually be a work in progress until further notice.

SPOILERS ABOUND. IF YOU INTEND TO WATCH THE SERIES, AND/OR HAVE NOT WATCHED THE LATEST EPISODE. DO NOT CONTINUE OR RISK SPOILING YOURSELF.
Likewise, insofar as the anime has revealed, I will not be spoiling any further than the anime.


The Fifth Holy Grail War

The Holy Grail War (for more information read Part II) is a event that usually happens every sixty years, as it takes that amount of time for the Holy Grail to accumulate enough mana to activate. However, the fifth Holy Grail War began a mere ten years after the fourth Holy Grail War. This is because the fourth Holy Grail War, chronicled in Fate/Zero, did not end with a conclusive victory, and thus the excess mana was kept until sufficient mana was accumulated to begin a fifth war.


Holy Grail - Great Grail and Lesser Grail

The true Holy Grail that has the power to grant wishes is known as the Great Grail. However, since the Great Grail cannot manifest itself in the human realm, a vessel known as the Lesser Grail is required to access it. The Lesser Grail, essentially is a container to house the Great Grail. Initially, it was a literal 'cup', but has henceforth been turned into a homunculus with means of protecting and managing itself after the initial 'cup' was destroyed in a prior war.


Avalon

Avalon is the hallowed scabbard of Excalibur, and is the catalyst used to summon Saber both in the fourth and fifth Holy Grail War. The holder of the scabbard is granted potent healing, allowing for critical and even fatal wounds to be rapidly healed. It is what allows Emiya Shirou to survive a stab in the heart by Lancer's Gae Bolg, and after being stabbed multiple times by Archer. Emiya Kiritsugu transplanted Avalon into Emiya Shirou in order to save his life as he found him dying in the Great Fire. It is less potent without the contract, but it still offers its limited immortality ability as long as Saber is in close proximity.


Please tell me in the comments if there's anything else mentioned in the show that you do not understand, and I'll try to address it here to the best of my abilities.
ONCE AGAIN, DO NOT VISIT THE WIKIA PAGE TO FIND ANSWERS AS YOU WILL SPOIL YOURSELF AND DESTROY THE TRUE EXPERIENCE OF THE SHOW.