Capital gains mean the profit earned by an individual on the sale of his investment in assets such as stocks, real estate, bonds, commodities, etc. Basically, it is the 'gain' made on 'capital investment'. In some tax jurisdictions — a country, state or city — capital gains are taxed if an individual sells an asset after holding it for a certain 'long' period. This period is often twelve months. However, it could also be defined differently for various assets. 
In India, 'long-term' and 'short-term' are defined by the Income Tax Act, 1961. While a holding period of one year is considered 'long-term' for equities, the same is two years for real estate. 
The Union Budget 2018 proposed to levy long-term capital gains tax (LTCG) of 10 per cent on gains exceeding Rs 100,000 from sale of equity shares. However, no change was made in the definition of short-term capital gains tax (STCG).
LTCG on sale of shares / stocks was removed in 2005, making India one of the most liberal stock market regimes. However, there were demands from a section of stakeholders that the LTCG tax on equities be brought back. The BSE had reportedly told the government that the revenue forgone on the LTCG tax exemption on listed securities could be as high as Rs 50,000 crore per year.
Another change that was made in the Union Budget 2018 was that an individual could get an exemption by investing long-term capital gains from the sale of house property in up to two house properties, against the earlier provision of investment in one house property with same conditions. However, the capital gains on the sale was restricted at Rs 2 crore for the exemption.
The LTCG and STCG tax rates also vary based on the asset class — they might be different for equities, real estate, bonds, mutual funds etc — and the income tax slab an individual falls under.