|"Is this all real? Or has this been happening inside my head?"
The topic of this article is of a real-life subject that has been mentioned "in-universe" in a canon source. The Harry Potter Wiki is written from the perspective that all information presented in canon is true (e.g., Hogwarts really existed), and, as such, details contained in this article may differ from real world facts.
Aspen (genus Populus) is a common name for certain tree species, some, but not all, of those that are classified by botanists in the section Populus, of the poplar genus.
Wand-quality aspen wood was white and fine-grained, and highly prized by all wand-makers for its stylish resemblance to ivory and its usually outstanding charmwork. The proper owner of the aspen wand was often an accomplished duellist, or destined to be so, for the aspen wand was one of those particularly suited to martial magic.
An infamous and secretive eighteenth-century duelling club, which called itself The Silver Spears, was reputed to admit only those who owned aspen wands. Garrick Ollivander often found that aspen wand owners were generally strong-minded and determined, more likely than most to be attracted by quests and new orders; this was a wand for revolutionaries.