Define prior public use in the context of patent law and also discuss exceptions to prior public use under Patents Act, 1970.

Prior public use in patent law refers to the use of an invention by the public in India before the priority date or filing date of a patent application, in such a manner that the invention becomes accessible to the public. If an invention has been publicly used prior to the filing of a patent application, it lacks novelty and is therefore not patentable. Under the Patents Act, 1970, prior public use is a ground for opposition and revocation, as provided under Sections 25 and 64. Public use does not necessarily require commercial exploitation; any non-secret use that makes the invention available to the public amounts to prior public use. However, there is an exception to this general rule. The Act provides that if an invention has been publicly worked in India within one year before the priority date by the patentee or applicant for the patent or by any third person from whom he derives the title or by the person who has obtained a consent to work the invention and such working of invention was only for the purpose of reasonable trial and it was necessary to effect such trial or working in public in view of the nature of the invention then such working of invention does not anticipate the invention (Section 32). In case of a prior disclosure by the inventor, the Patents Act provides a one-year grace period for filing a patent application if the invention has been described in front of a learned society or published during the transactions of such learned society. The grace period is also available for conducting reasonable trials such as data generation for regulatory approval; it is not available where an invention is being sold or commercially worked in India. However, any use or publication of an invention after filing a provisional patent application in India will not be considered anticipation. Similarly, the grounds relating to public display [Sections 31(a), 31 (b) and 31(c)], public working (Section 32) and traditional knowledge [Section 3(p)] are major considerations when determining novelty. An invention can also be anticipated by knowledge, either oral or in any other form existing in a local or indigenous community in India or elsewhere. The general factors considered for anticipation assessment may be relevant in selection invention cases. In selection inventions, the selection of specific dimensions, ranges of values or parameters within (prior) larger areas based on new characteristics and unknown properties is considered to be an invention. While the Indian Patent Office (IPO) does not expressly state that selection patents are unpatentable in India, a combined reading of Sections 3(d) and 2(1) (ja) appears to have a strict standard regarding patentability of selection inventions. Exceptions to Prior Public Use under the Patents Act, 1970 are as under: Use for Experiment or Trial Use of the invention solely for experiment or trial, including to test its utility or improve it, does not constitute prior public use. Use in Government-approved Institutions Use of the invention at government-controlled or government-approved institutions for research or experimentation is excluded from prior public use. Secret or Confidential Use Use of the invention in secrecy, such as internal testing or confidential trials, does not amount to public use since the invention is not made available to the public. Use by the True and First Inventor for Reasonable Period Use by the inventor himself, in good faith and for a reasonable time prior to filing, solely for development or testing, is not considered prior public use. Display at Exhibition Display of an invention at a notified exhibition or publication of its description therein does not amount to prior public use, provided the patent application is filed within the prescribed time.