What with KN^4 posts and 1級 Grammar, we've been giving you an awful lot of useful Japanese lately, and I imagine that all of you wish we'd get back to our old, extremely impractical ways.
So in that spirit, if you find a way to use today's 四字 in a casual conversation, you have my undying respect.
1. Paradise, specifically the pure land inhabited by Amitabha, also known as Sukhavati.
According to the Mayahana school, Amitabha, the Buddha of Infinite Light, was once a bodhisattva called Dharmakara, with aspirations for creating a new Buddha realm out of his Buddha merit. He's credited with 48-vows which defined the realm, and laid out conditions for getting into said realm.
Though that might sound intense, Amitabha's school of thought (known as Pure Land Buddhism) was actually a reaction to what he felt was the difficulty of attaining Nirvana through the traditional methods of meditation... so instead, all you had to do to get into the Pure Land was to call Amitabha's name, like ten times or so during your life (18th vow) or to summon Amitabha and his disciples to your death bed.
This meant that ANYONE, including impoverished, or prostitutes, or any social outcast who had previously been denied the chance to receive spiritual services could appeal to Amitabha and have a chance of entering paradise. It began in India, traveled through Pakistan, Afghanistan, Central Asia, and then ran the circuit from China, to Vietnam, to Korea, to medieval Japan, where it became extremely popular for the reasons mentioned above.
(Of course, the 48 vows also stipulate that devotion to Amitabha is the ONLY way into the paradise, which DT Suzuki might say was the EXACT kind of deification that the Buddha warned about when he said "If you meet the Buddha on the road, kill him.")
In any case, it's known as 浄土教 in Japanese, and I feel fairly confident in saying that the only time you'll ever be able to use it is when you're talking about this school of Buddhism.
The aristocrats and nobles of Heian Era Japan believed that after death, praying to Amitabha would allow them to be reborn unto Sukhavati.
I spent a long time looking over the site where I found this last picture, and am 98% sure that there's nothing dirty going on here...