The National Association for Gifted Children explains Twice Exceptionality (2e) as follows:
What’s not often well-known or well-understood is that students who are gifted may also have a special need or disability— just as students with disabilities may also be gifted. The term “twice-exceptional,” also referred to as “2e,” is used to describe gifted children who, have the characteristics of gifted students with the potential for high achievement and give evidence of one or more disabilities as defined by federal or state eligibility criteria. These disabilities may include specific learning disabilities (SpLD), speech and language disorders, emotional/behavioral disorders, physical disabilities, autism spectrum, or other impairments such as attention deficit hyperactivity disorder (ADHD)
Like other gifted learners, 2e students are highly knowledgeable and talented in at least one particular domain. However, their giftedness is often overshadowed by their disabilities, or these students may be able to mask or hide their learning deficits by using their talents to compensate. Sometimes a twice-exceptional child’s special education needs are overlooked until adolescence or later, or are never identified throughout his or her life.
Twice-exceptional children often find difficulty in the school environment, where organization, participation, and long-term planning play a role. They can be highly creative, verbal, imaginative, curious, with strong problem-solving ability, and a wide range of interests or a single, all-consuming expertise. However, at school, they may have difficulty keeping up with course rigor, volume, and demands–resulting in inconsistent academic performance, frustration, difficulties with written expression, and labels such as lazy, unmotivated, and underachiever. All this may hinder their excitement for school and be detrimental to their self-efficacy, self-confidence, and motivation.
(see https://www.nagc.org/resources-publications/resources-parents/twice-exceptional-students)