...

You can also say "unregistered exclusive license" or "contractual exclusive license."

I realize that a literal translation would be something like "preferential license” or "priority license," but I think this license is meant to grant the same rights as an "exclusive license," but without the formalities of an "exclusive license". The difference seems to be that a contractual exclusive license is not grounded in the statute, but rather is created by contract. It is not registered with the Patent Office like a 専用実施権, which is why I think the contrast with a "registered exclusive license" is appropriate.

The following company seems to have translated it as "priority license," but I think if you read the provision it would make more sense as some type of "exclusive license" (why cancel a "priority license" before granting someone else a license unless that "priority license" was in fact exclusive?):
http://www.nanocarrier.co.jp/en/news/topics/pdf/e20080512.pd...
(See #2 on p. 12)

http://www.pref.akita.jp/gakujutu/tizai/3/gaiyou2.html
専用実施権は、業として特許発明の内容を「独占排他的」に実施できる権利であり、同じ内容で複数人に設定することはできません。専用実施権の設定を受けた者は、自分だけが特許発明の内容を独占できるという極めて強固な権利です（特許法第７７条）。
　通常実施権は、業として特許発明の内容を実施できる権利であり、同じ内容で複数人に許諾することができます。専用実施権のように特許発明の内容を独占することはできません（特許法第７８条）が、使いやすさなどから実施許諾の中で最も多くみられる実施権です。
　独占的通常実施権（優先実施権ともいう）は、特許法上規定はありませんが、実務上広く認められている実施権です。専用実施権同様、業として特許発明の内容を「独占排他的」に実施できる権利ですが、法律上の専用実施権ではなく、実施許諾契約の中で「独占的権利」である旨を定めた「通常実施権」の一種と考えられています。
　なお、法律上は、「専用実施権」の場合は「設定」と、「通常実施権」の場合は「許諾」と呼んでいますが、実務上はどちらも「実施許諾」と呼んでいます。

http://www.furutani.co.jp/cgi-bin/term.cgi?title=�Ɛ�I���{��
なお、専用実施権は、特許庁の原簿に登録しなければ効力を生じない（特許法９８条１項２号）。実務的には、ライセンス契約書において「独占的」である旨を、当事者間で定めておき、特許庁原簿への登録を行わない場合もある。このような場合、法的には、専用実施権と呼ぶことはできず、”独占的通常実施権”と呼ばれている。”独占的通常実施権”を有する者が、差し止め請求、損害賠償請求を行使できるか否かは、議論が分かれている。

http://www.google.com/url?sa=t&source=web&cd=1&sqi=2&ved=0CB...
"Patent owner may grant license to third parties. Patent license is generally classified into three
categories. The first category is non-exclusive license (tsujou-jisshiken), under which the licensee is
entitled to contractual non-exclusive right to exploit the patented invention. A non-exclusive license may
be registered with JPO for the purpose of perfection. The second category is non-registered exclusive
license (dokusenteki-tsujou-jisshiken), under which the licensee is entitled to contractual exclusive right to
exploit the patented invention. A non-registered exclusive license may be registered with JPO as a
non-exclusive license for the purpose of perfection. The third category is registered exclusive license
(senyou-jisshiken), under which the licensee is entitled to absolute exclusive right to exploit the patented
invention. Registered exclusive license becomes effective upon its registration with JPO. If the patent
owner grants registered exclusive license, it may not exploit the patented invention unless the holder of
the registered exclusive license grants back a license to the patent owner. Either the patent owner or the
holder of registered exclusive license may bring a lawsuit against infringement of the patent in its own
name."

http://www.iip.or.jp/e/e_summary/pdf/detail2003/e15_09.pdf
See V(1) on p. 4.

http://www.europeanlawyer.co.uk/referencebooks_2_75.html
A patent licensee is generally classified into one of three categories:
(1)
registered exclusive licensee (Senyo-Jisshiken);
(2)
non-registered exclusive licensee (Dokusenteki-Tsujo-Jisshiken); or
(3)
non-exclusive licensee (Hidokusenteki-Tsujo-Jisshiken).
A registered exclusive licensee, the licence of which must be registered in the Patent Register at the JPO in order to take effect, is granted a right to bring a law suit seeking an injunction and compensation for damages under the Patent Law. A non-registered exclusive licensee can claim damages incurred by itself from infringers without the licence being registered. However, court decisions and theories are not unified with regard to whether or not a nonregistered exclusive licensee can demand an injunction in subrogation of a patent owner. Neither the Patent Law nor court precedents have granted a non-exclusive licensee the right to seek an injunction against and compensation for damages from a patent infringer.

https://www.aippi.org/download/yearbooks/Annuaire 1996_IV.pd...
see p. 229: There are two types of exclusive licenses in Japan: one is a statutory exclusive license "SENYO JISSHIKEN" which becomes effective only when registered in the Patent Office (hereinafter called "Statutory Exclusive License"); the other is a contractual exclusive license ("Contractual Exclusive License").

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Note added at 5 days (2011-02-26 23:00:39 GMT)
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The full text of this article refers to the license as a "preferential license," so there's another option for you:

http://heinonline.org/HOL/LandingPage?collection=journals&ha...
"Alternatively, the company can request from the university president a 10-year renewable preferential license, 115 which is essentially an exclusive license with development and royalty payment obligations and government 'march in' rights (i.e., compulsory licensing rights in emergency situations)." n115 Japanese: yuu-sen jisshi ken.