In terms of online presence, aesthetics refer to a specific colour scheme, the type of images you post, and/or both. It should be something that makes sense to your specific brand and should always stay true to and be representative of brand values.
In the age of social media, how you present your content matters. Having posts and an overall theme that is curated beautifully can be the make or break of why someone would follow you.
A clear aesthetic online is beneficial to a business because simply put: it makes people happy. Having visually appealing content attracts people and keeps them looking. When people love your brand and the content you put out, seeing new posts is exciting.
Some things to keep in mind when determining your theme or aesthetic:
What are your brand values?
What product or service are you selling?
Who is your target customer?
Does your brand take more of an exciting maximalist approach or that of a more simple minimalism?
Do you have a colour scheme? If not, what type of colours speak best to you?