A bungalow is a type of house that has specific architectural characteristics, though the term's usage can vary somewhat by region.
Traditionally, and most commonly, a bungalow is characterized as:
(ų) A single-story dwelling: This is a key feature. All primary living spaces are on one floor. Some bungalows might have a small upper room or attic space built into the roof (often called a 1.5-story bungalow or chalet bungalow), but the main living area is on the ground floor.
(Ŵ) Typically with a sloping roof: Bungalows often feature low-pitched, hipped or gabled roofs, often with wide eaves.
(ŵ) Often with a verandah or porch: A covered porch or verandah is a common feature, especially in traditional bungalow styles that originated in India (from Bengali \textit{bangla}, meaning "belonging to Bengal").
(Ŷ) Detached or semi-detached: Usually a standalone house, though the term can sometimes apply to semi-detached structures of similar style.
(ŷ) Compact and informal layout: Compared to larger, more formal houses.
Let's evaluate the options:
(Ÿ) (a) A multi-story residential unit: This contradicts the typical single-story nature of a bungalow. Multi-story units are townhouses, apartments, or larger houses.
(Ź) (b) A single-story dwelling, typically with a sloping roof: This accurately describes the core characteristics of a bungalow.
(ź) (c) An attached housing unit with shared walls: This describes row houses, townhouses, or semi-detached houses, not typically a bungalow (which is usually detached).
(Ż) (d) A high-density apartment building: This is completely different from a bungalow, which is a low-density housing type.
Therefore, a bungalow is best characterized as a single-story dwelling, typically with a sloping roof.
\[ \boxed{\text{A single-story dwelling, typically with a sloping roof}} \]