Wikipedia says: Quantum computing is a type of computation whose operations can harness the phenomena of quantum mechanics, such as superposition, interference, and entanglement. Devices that perform quantum computations are known as quantum computers.
The rest of the article is a bit too technical. The Keysight article Quantum Computing: Top 5 Questions Answered (November 9, 2022; AuthorJenn Mullen; 8 min read) presents the subject in a more comprehensible terms for non specialists.
For me the most useful part to understand was the following 2 paragraphs that also introduce a new word to me: decoherence.
Noise and decoherence in quantum computers
Realizing the vision for quantum computing requires that researchers develop qubits that are as reliable as their binary counterparts. This process is known as decoherence and is a result of environmental changes like fluctuations in electric and magnetic field fluctuations and radiation from warm objects. Decoherence can even result from the passive act of observing particulate interactions.
Qubits can only store memory for less than one minutes before decoherence sets in, resulting in computing systems that are highly unstable even in the most controlled environments. Currently, quantum computers operate in environments cooled to near absolute zero temperatures to minimize decoherence. Quantum computing researchers are actively investigating ways to minimize or suppress decoherence, produce shelf-stable qubits, and scale processors up past the dozen qubits currently possible today.