Oricon puts out Japanese music charts, similar to the Billboard charts in the US. The name "Oricon" is derived from the English words "original confidence".

Oricon maintains several ranking lists and publishes them on its website. While paying customers have access to the full lists, a slimmed down version is available for free (the Weekly Top 50 for singles and albums).

HIGHEST 1ST WEEK SALES FOR SINGLES (OVERALL)
    1. TVXQ! - BREAK OUT! (2010) 255,917
    HIGHEST 1ST WEEK SALES FOR ALBUMS (OVERALL)
      1. BoA - VALENTI (2003) 615,218
      2. BoA - BEST OF SOUL (2005) 489,067
      3. TVXQ! - BEST SELECTION 2010 (2010) 412,861
      4. BoA - LOVE & HONESTY (2004) 296,781
      5. TVXQ! - TIME (2013) 243,827
      6. TVXQ! - WITH (2014) 233,216
      7. Girls' Generation - GIRLS' GENERATION (2011) 231,553
      HIGHEST 1ST WEEK SALES FOR SINGLES (BOY GROUP)
        1. TVXQ! - BREAK OUT! (2010) 255,917
        2. TVXQ! - Why? (Keep Your Head Down) (2011) 231,498
        3. TVXQ! - 時ヲ止メテ (2010) 195,250
        4. TVXQ! - Stand by U (2009) 182,068
        HIGHEST 1ST WEEK SALES FOR ALBUMS (BOY GROUP)
          1. TVXQ! - BEST SELECTION 2010 (2010) 412,861
          2. TVXQ! - TIME (2013) 243,827
          3. TVXQ! - WITH (2014) 233,216
          4. TVXQ! - TREE (2014) 224,796
          5. TVXQ! - TONE (2011) 204,980
          6. TVXQ! - The Secret Code (2009) 157,954
          7. TVXQ! - FINE COLLECTION~Begin Again~ (2017) 130,447
          HIGHEST 1ST WEEK SALES FOR ALBUMS (GIRL GROUP)
            1. Girls' Generation - Girls’ Generation (2011) 231,553
            2. Girls' Generation - Love & Peace (2013) 129,255

            A typical Oricon week:

            Almost all Japanese singles or albums are released on Wednesdays, and there is a reason behind this. I'm going to use KARA's Mister as an example. The single was released on August 11 2010, but it actually hit the shelves on August 10. The Oricon data released on August 11 is actually a reflection of the sales of the single from Tuesday, August 10. Likewise, the Oricon data released on Thursday, August 12, reflects Wednesday's sale. The typical Oricon week for a new release looks like this: TuesdayWednesdayThursdayFridaySaturday, and Sunday, then the sales from these six days are compiled into the weekly chart. For old releases (read: after first week of release), the weekly chart consists of sales from all seven days of the week. In order to achieve the highest sale possible on the weekly chart, artists usually release their work on Wednesdays.

            When is the Oricon chart usually updated?

            The daily charts are usually updated around 7PM JST, and the weekly charts around 5PM on every Tuesday/Wednesday.

            Regarding the weekly "add-ons/weekend boost" in sales:

            At the end of the week, Oricon will put together the data from the daily rankings PLUS additional reported sales from retailers that only send in their data once a week. This is why there is usually a small boost in the weekly charts.

            About Oricon only counts 30% of CDs sold at non-Oricon vendors:

            Starting September 01, 2009, Oricon implemented a new rule which only accounts 30% of a single/album's sales when a non-Oricon establishment sells that single/album. In other words, if for instance copies of a single/album were being sold at a meet and greet, a handshaking event, or during merchandise sales at the front of concert venues (where you are able to buy your concert goods like uchiwas and t-shirts before the concert doors open and such), than Oricon will only take into account 30% of the sales that the event "sold" during that time. If at the event 5,000 copies of a single/album were sold, only 30% of the 5,000 copies would be added onto the Oricon sales figure. In other words, only 1,500 copies of the 5,000 copies sold at the event would count towards the Oricon charts. Oricon began this rule because there was no official way for them to know the amount of copies actually sold at the time of the event. This rule is to prevent fraudulent record sales that record companies may give in order to boost their artist's sales figure.