Products are located mainly in the following tables:
wp_posts table with post_type like product (or product_variation),
wp_postmeta table with post_id as relational index (the product ID).
wp_wc_product_meta_lookup table with product_id as relational index (the post ID) | Allow fast queries on specific product data (since WooCommerce 3.7)
wp_wc_order_product_lookuptable with product_id as relational index (the post ID) | Allow fast queries to retrieve products on orders (since WooCommerce 3.7)
Product types, categories, subcategories, tags, attributes and all other custom taxonomies are located in the following tables:
wp_terms
wp_termmeta
wp_term_taxonomy
wp_term_relationships - column object_id as relational index (the product ID)
wp_woocommerce_termmeta
wp_woocommerce_attribute_taxonomies (for product attributes only)
wp_wc_category_lookup (for product categories hierarchy only since WooCommerce 3.7)
Product types are handled by custom taxonomy product_type with the following default terms:
simple
grouped
variable
external
Some other product types for Subscriptions and Bookings plugins:
subscription
variable-subscription
booking
Since Woocommerce 3+ a new custom taxonomy named product_visibility handle:
The product visibility with the terms exclude-from-search and exclude-from-catalog
The feature products with the term featured
The stock status with the term outofstock
The rating system with terms from rated-1 to rated-5
Particular feature: Each product attribute is a custom taxonomy…
References:
Normal tables: Wordpress database description
Specific tables: Woocommerce database description