An expert is somebody who has a broad and deep understanding and competence in terms of knowledge, skill and experience through practice and education in a particular field or area of study. Informally, an expert is someone widely recognized as a reliable source of technique or skill whose faculty for judging or deciding rightly, justly, or wisely is accorded authority and status by peers or the public in a specific well-distinguished domain. An expert, more generally, is a person with extensive knowledge or ability based on research, experience, or occupation and in a particular area of study. Experts are called in for advice on their respective subject, but they do not always agree on the particulars of a field of study. An expert can be believed, by virtue of credentials, training, education, profession, publication or experience, to have special knowledge of a subject beyond that of the average person, sufficient that others may officially rely upon the individual's opinion on that topic. Historically, an expert was referred to as a sage. The individual was usually a profound thinker distinguished for wisdom and sound judgment.

भौतिक साक्ष्यों के परिक्षण एवम प्रतिवेदन को जो व्यक्ति न्यायालय के समक्ष तथ्यों को लेकर जाता है, उस मुख्य व्यक्ति को विशेषज्ञ कहते हैं। विशेषज्ञ प्रमाणित किए गए सभी परिक्षणों को अच्छे तरीक़े से जानकारी एकत्रित करने के अलावा सम्भंदित साहित्य में अपने से वरिष्ठ सहयोगियों की सहायता लेकर भी रिपोर्ट तैयार कhdududussusueusbssbdndnsnsnsnर सकता है। विशेषज्ञ अपनी शैश्निक योग्यता, परीक्षण का प्रकार एवम अवधि, सम्बन्धी विषय में परिक्षण कार्य का अनुभव आदि के बल पर न्यायालय में अपनी योग्यता सिद्ध करता है।