koj, daij, meikyo, shinmeikai, gg5, OED
https://ja.wikipedia.org/wiki/ブルーフィルム

overly specific explanation, i think

@@ -11,0 +12 @@
+<gloss>blue movie</gloss>
@@ -13 +14 @@
-<gloss g_type="expl">early (1950s-) type of hardcore pornographic film usually filmed on 8 or 16mm film and often in black market circulation</gloss>
+<gloss g_type="expl">pornographic movie (esp. one screened secretly)</gloss>

@@ -13 +13 @@
-<gloss g_type="expl">early (1950's-) type of hardcore pornographic film usually filmed on 8 or 16 mm film and often in black market circulation</gloss>
+<gloss g_type="expl">early (1950s-) type of hardcore pornographic film usually filmed on 8 or 16mm film and often in black market circulation</gloss>

https://books.google.com/books?id=s7-_Gon5-
a0C&pg=PA300&dq=Japanese+%22blue+film%22&hl=en&sa=X&ved=
0ahUKEwjFkqry9IHZAhXL6oMKHZhpARUQ6AEIJzAA#v=onepage&q=Ja
panese%20%22blue%20film%22&f=false
"blue film - earlier American term for hard-core 
pornographic film"
https://books.google.com/books?id=8sc-
AQAAIAAJ&q=Japanese+%22blue+film%22&dq=Japanese+%22blue+
film%22&hl=en&sa=X&ved=0ahUKEwjFkqry9IHZAhXL6oMKHZhpARUQ
6AEIXzAL
"Blue films" (buru eiga) are erotic films roughly 
distinguished from "pink films" (pinky eiga) in official 
circles by the absence of a story element."
https://books.google.com/books?
id=v5LZ30HI6dsC&pg=PA173&dq=%22blue+film%22+porn&hl=en&s
a=X&ved=0ahUKEwierOG29YHZAhUL24MKHUaVDIoQ6AEIPjAE#v=onep
age&q=%22blue%20film%22%20porn&f=false
"In the recent book Nihon eigha ha, ima (Japanese film 
today), Sano Shinichi dedicates an engaging chapter to 
the fifty-year history of Japanese pornographic film and 
video. The industry emerged in the late 1940s and boomed 
in the early 1950s. First there was blue film, a rag-tag 
operation of amateurs and misfits that produced twenty-
minute shorts. Blue film was followed by pink film, 
which produced soft-porn sponsored by the major film 
companies to offset the loss of revenue from declining 
ticket sales brought about by the popularity of 
television. ... Sano's blue-pink-adult trajectory offers 
a good start at historicizing the links among the three 
dominant moments of pornography."

@@ -13 +13 @@
-<gloss g_type="expl">early (1950's-) type of pornographic film usually filmed on 8 or 16 mm film and often in black market circulation</gloss>
+<gloss g_type="expl">early (1950's-) type of hardcore pornographic film usually filmed on 8 or 16 mm film and often in black market circulation</gloss>

https://dot.asahi.com/wa/2016120100343.html?page=1
"かつて「風俗小型映画」と呼ばれるジャンルがあった。性的、わい
せつな映像作品を指す俗称「ブルーフィルム」（16ミリや8ミリ）と
言ったほうがわかりやすいかもしれない。
昭和27（1952）年から昭和31年くらいまでが全盛だったとされる。"
https://www.npa.go.jp/hakusyo/s53/s530600.html
”山口組系暴力団の幹部（46）が、ブルーフィルムの密造販売によっ
て組の活動資金を得ようと企て、最新式の自動プリンター、自動現像
装置その他の製作資機材一式を購入し、配下組員らを使って約5年の
間に35万巻（末端価格で約49億2,800万円）に上るブルーフィルムを
密造し、4系列33団体の暴力団を通じて全国各地に販売していた事犯
で、暴力団員51人を含む被疑者96人を検挙するとともにブルーフィル
ム、製作資機材等トラック3台分を押収した（愛知）。"
http://bungaku.cocolog-
nifty.com/barazoku/2005/09/post_7d44.html
"ブルーフィルムは、ほとんどヤクザさんが製作していて、比較的に
取締りがゆるい、四国の山中などで作られることが多かったよう
だ。"
wiki: "主としてポルノグラフィを題材とした、すなわち性的・猥褻
な映像作品、または映像媒体でのポルノグラフィを指す俗称。以下の
項目等が現在の主流であるが、日本では特に、かつて温泉宿などでの
秘密上映会用に多数製作されていた短編の猥褻映画を指すことが多
い。8ミリフィルムが用いられており、多くは非合法であった。現在
は同様の形では存続していない。"
enwiki: "Blue film, term used for erotic films in 
underground distribution in India"
I also get hits for the same "phenomenon" in China

@@ -13 +13 @@
-<gloss>porno(graphic) film</gloss>
+<gloss g_type="expl">early (1950's-) type of pornographic film usually filmed on 8 or 16 mm film and often in black market circulation</gloss>