Results of Operations
The following describes the line items set forth in our consolidated statements of operations. A discussion of changes in our results of operations during the year ended December 31, 2018 compared to the year ended December 31, 2017 has been omitted from this Annual Report on Form 10-K, but may be found in “Item 7.
Management’s Discussion and Analysis of Financial Condition and Results of Operations” in our Annual Report on Form 10-K for the year ended December 31, 2018, filed with the SEC on February 5, 2019, which discussion is incorporated herein by reference and which is available free of charge on the SEC’s website at www.sec.gov.
Net Revenue. Net revenue is generated from sales of radio-frequency, analog and mixed-signal integrated circuits for the connected home, wired and wireless infrastructure, and industrial and multi-market applications. A significant portion of our sales are to distributors, which then resell our products.
Cost of Net Revenue. Cost of net revenue includes the cost of finished silicon wafers processed by third-party foundries; costs associated with our outsourced packaging and assembly, test and shipping; costs of personnel, including stock-based compensation, and equipment associated with manufacturing support, logistics and quality assurance; amortization of acquired developed technology intangible assets and inventory step-ups to fair value; amortization of certain production mask costs; cost of production load boards and sockets; and an allocated portion of our occupancy costs.
Research and Development. Research and development expense includes personnel-related expenses, including stock-based compensation, new product engineering mask costs, prototype integrated circuit packaging and test costs, computer-aided design software license costs, intellectual property license costs, reference design development costs, development testing and evaluation costs, depreciation expense and allocated occupancy costs.
Research and development activities include the design of new products, refinement of existing products and design of test methodologies to ensure compliance with required specifications. All research and development costs are expensed as incurred.
Selling, General and Administrative. Selling, general and administrative expense includes personnel-related expenses, including stock-based compensation, amortization of certain acquired intangible assets, third-party sales commissions, field application engineering support, travel costs, professional and consulting fees, legal fees, depreciation expense and allocated occupancy costs. Impairment Losses. Impairment losses consist of charges resulting from the impairment of acquired intangible assets.
Restructuring Charges. Restructuring charges consist of severance, lease and leasehold impairment charges, and other charges related to restructuring plans. Interest and Other Income (Expense), Net. Interest and other income (expense), net includes interest income, interest expense and other income (expense). Interest income consists of interest earned on our cash, cash equivalents and restricted cash balances. Interest expense consists of interest accrued on debt. Other income (expense) generally consists of income (expense) generated from non-operating transactions.
Income Tax Provision (Benefit). We make certain estimates and judgments in determining income tax expense for financial statement purposes. These estimates and judgments occur in the calculation of certain tax assets and liabilities, which arise from differences in the timing of recognition of revenue and expenses for tax and financial statement purposes and the realizability of assets in future years.
The following table sets forth our consolidated statement of operations data as a percentage of net revenue for the periods indicated:
Table:
 |  | Years Ended December 31,
 | 2019 | 2018
Net revenue | 100% | 100%
Cost of net revenue | 47 | 46
Gross profit | 53 | 54
Operating expenses: |  | 
Research and development | 31 | 31
Selling, general and administrative | 28 | 26
Impairment losses | - | 1
Restructuring charges | 1 | 1
Total operating expenses | 60 | 59
Loss from operations | (7) | (5)
Total interest and other income (expense), net | (3) | (4)
Loss before income taxes | (10) | (9)
Income tax benefit | (4) | (2)
Net loss | (6)% | (7)%


Question: What are research and development activities?
Answer: the design of new products, refinement of existing products and design of test methodologies to ensure compliance with required specifications.