The Khmer (pronounced 'Kmai' in this context, unlike the Khmer Rouge pronounced 'Kmair') New Year took place on April 13-16.
Unlike neighbouring Thailand and Laos, which have huge country-wide water fights to celebrate Songkran, Cambodia has family-focused festivities for three days, followed by a further two days for 'young lovers' to take off work.
As you can imagine, prices everywhere go wayyy up during this time. For instance, my bus ticket was increased by $4 from Siem Reap to Sihanoukville - the ticket agent was mortified when he told me this. 'Same goes for locals, so sorry miss. I understand if you don't book with us...' No worries, man.
I was on Koh Ta Kiev island for most of it, so I didn't partake in the festivities, but I could hear the music pumping from Sihanoukville and see the lights and fireworks.
It's mostly a time when people get a proper vacation from work and return to the provinces from the city to be with family to eat and drink and party together.
Sounds kind of like our New Years ;)