A patent is a set of exclusive rights granted by a state (national government) to an inventor or their assignee for a limited period of time in exchange for a public disclosure of an invention.
Patent claims
are the part of a patent or patent application that defines the scope of protection granted by the patent. The claims define, in technical terms, the extent of the protection conferred by a patent, or the protection sought in a patent application. The claims are of the utmost importance both during prosecution and litigation. A patent is a right to exclude others from making, using, selling or offering for sale the subject matter defined by the claims. In order to exclude someone from using a patented invention in a court, the patent owner, or patentee, needs to demonstrate that what the other person is using falls within the scope of a claim of the patent

The fewer the limitations in a claim, the more likely it is that the claim will cover or "read on" what came before and be rejected during examination or found to be invalid at a later time for lack of novelty. On the other hand, the more the limitations in a claim, the more difficult it is that the right will exclude others from using the subject matter.

For example, when a pencil whose cross-sectional shape is a hexagon has been invented so that it would not roll on a desk, a claim could define the pencil as “a pencil that does not roll”, which is likely to be rejected during examination, or otherwise as “a pencil whose cross-sectional shape is a hexagon”, which could hardly exclude others from designing around such as making pencils having pentagonal or quadrangular cross sections.

Accordingly, it is more valuable to obtain claims that include the minimal set of limitations that differentiate an invention over what came before, i.e. the so-called prior art.
Examination Guideline of Patent
A patent application must include one or more claims defining the invention which must be new, non-obvious, and useful or industrially applicable. Compared with novelty and industrial applicability, examination of non-obviousness is not quite simple.

Novelty and non-obviousness are examined based on publicly known materials, for example, patent publication, product in public use or on sale, invention published by an advertisement, and on-line publication.

During the novelty examination, a decision is made if the claimed invention is identical with that described in the publicly known materials before the date of filing.

During the non-obviousness examination, a decision is made if the claimed invention is similar to that of the publicly known materials or would have been obvious to the person skilled in the art in view of the publicly known materials. Most of the rejections come from the non-obviousness examination.
Comparison of Patent and Utility Model
In Korean patent practice, patent term is 20 years from the filing date of the earliest Korean application to which priority is claimed, while utility model term is 10 years from the filing date. In a patent, a method can be claimed as well as a device, which is not allowed in a utility model. In a utility model, a subject to be claimed is restricted to device.

Comparing patent with utility model, patent has a longer term and is capable of claiming method claims. In this regard, patent application might be preferable to utility model application in spite of slightly higher cost