The term 'inventive step', predominantly used in Europe, is one of the requirements of patentability - though what constitutes an inventive step may depend on the nature of the invention. Inventive step is a requirement present in most patent laws, according to which an invention should be sufficiently inventive—i.e., non-obvious—in order to be patented.
The purpose of the inventive step, or 'non-obviousness', requirement is to encourage innovation rather than incremental improvements. Designing a larger screen for a smart phone would not likely be seen as innovative, it needs to more of a step forward. You can read lots more on the subject of inventive step here on the gov.uk website.
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